:root {
        --color-black: #050505;
        --color-dark-grey: #111111;
        --color-green: #00ff41;
        --color-red: #ff073a;
        --color-white: #f0f0f0;
        --color-gold: #ffd700;
        --color-silver: #c0c0c0;
        --color-bronze: #cd7f32;
        --color-blue: #00bfff;
        --color-purple: #9932cc;
        --color-orange: #ff8c00;
        --color-pink: #ff69b4;
        --color-cyan: #00ffff;
        --color-yellow: #ffff00;
        --font-primary: "Exo 2", sans-serif;
        --font-secondary: "Roboto Mono", monospace;
      }

      * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
      }

      body {
        background-color: var(--color-black);
        color: var(--color-white);
        font-family: var(--font-secondary);
        min-height: 100vh;
        display: flex;
        overflow-x: hidden;
      }

      /* Header Controls */
      .header-controls {
        display: flex;
        align-items: center;
        gap: 15px;
        position: fixed;
        top: 20px;
        right: 20px;
        z-index: 10000;
      }

      /* Mobile header controls */
      @media (max-width: 768px) {
        .header-controls {
          top: 10px;
          right: 10px;
          flex-direction: column;
          gap: 10px;
        }

        #resetProgressBtn {
          position: relative;
          top: 0;
          right: 0;
          padding: 8px 12px;
          font-size: 0.8rem;
        }
      }

      .music-dropdown {
        position: relative;
        display: inline-block;
      }

      .music-dropdown-content {
        display: none;
        position: absolute;
        right: 0;
        background-color: var(--color-dark-grey);
        min-width: 200px;
        box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
        z-index: 10002;
        border-radius: 8px;
        border: 1px solid rgba(0, 255, 65, 0.2);
        padding: 10px;
        margin-top: 5px;
      }

      .music-dropdown-content a {
        color: var(--color-white);
        padding: 12px 16px;
        text-decoration: none;
        display: flex;
        justify-content: space-between;
        align-items: center;
        border-radius: 4px;
        transition: background-color 0.3s ease;
      }

      .music-dropdown-content a:hover {
        background-color: var(--color-black);
        color: var(--color-green);
      }

      .music-dropdown-content a.playing {
        color: var(--color-green);
        background-color: rgba(0, 255, 65, 0.1);
      }

      .music-dropdown-content a.playing .fa-volume-high {
        color: var(--color-green);
      }

      .btn {
        padding: 10px 20px;
        border: none;
        border-radius: 6px;
        font-family: var(--font-secondary);
        font-weight: 600;
        cursor: pointer;
        transition: all 0.3s ease;
        text-decoration: none;
        display: inline-flex;
        align-items: center;
        gap: 8px;
        font-size: 0.9rem;
      }

      .btn-secondary {
        background-color: var(--color-green);
        color: var(--color-black);
      }

      .btn-secondary:hover {
        background-color: #00cc33;
      }

      .music-indicator {
        position: absolute;
        top: 60px;
        right: 10px;
        background: #ffffff;
        color: var(--color-green);
        padding: 10px 16px;
        border-radius: 6px;
        font-size: 14px;
        font-weight: bold;
        box-shadow: 0 4px 15px rgba(0, 255, 65, 0.6);
        z-index: 9999;
        animation: bounce 1s infinite;
        display: flex;
        align-items: center;
        gap: 8px;
      }

      .music-indicator::before {
        content: "";
        position: absolute;
        top: -12px;
        right: 25px;
        width: 0;
        height: 0;
        border-left: 10px solid transparent;
        border-right: 10px solid transparent;
        border-bottom: 12px solid #ffffff;
      }

      .music-indicator i {
        color: var(--color-green);
        font-size: 16px;
      }

      @keyframes bounce {
        0%,
        100% {
          transform: translateY(0);
        }
        50% {
          transform: translateY(-6px);
        }
      }

      /* Auth Modal */
      .modal {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        z-index: 10000;
        display: flex;
        align-items: center;
        justify-content: center;
      }

      .modal-overlay {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: rgba(0, 0, 0, 0.8);
        backdrop-filter: blur(5px);
      }

      .modal-content {
        background: var(--color-dark-grey);
        border: 1px solid rgba(255, 255, 255, 0.1);
        border-radius: 15px;
        padding: 2rem;
        max-width: 400px;
        width: 90%;
        position: relative;
        z-index: 1;
      }

      .close {
        position: absolute;
        top: 1rem;
        right: 1.5rem;
        color: #aaa;
        font-size: 2rem;
        cursor: pointer;
        transition: color 0.3s ease;
      }

      .close:hover {
        color: var(--color-white);
      }

      .auth-tabs {
        display: flex;
        margin-bottom: 2rem;
        border-bottom: 1px solid rgba(255, 255, 255, 0.1);
      }

      .auth-tab {
        flex: 1;
        padding: 1rem;
        background: none;
        border: none;
        color: #aaa;
        cursor: pointer;
        transition: all 0.3s ease;
        font-family: var(--font-secondary);
      }

      .auth-tab.active {
        color: var(--color-green);
        border-bottom: 2px solid var(--color-green);
      }

      .auth-form h2 {
        color: var(--color-white);
        font-family: var(--font-primary);
        text-align: center;
        margin-bottom: 2rem;
        font-size: 1.5rem;
      }

      .btn-google {
        background: var(--color-white);
        color: var(--color-black);
        border: none;
        width: 100%;
        margin-bottom: 1rem;
        cursor: pointer;
      }

      .btn-google:hover {
        background: #f0f0f0;
      }

      .divider {
        text-align: center;
        margin: 2rem 0;
        position: relative;
        color: #666;
      }

      .divider::before {
        content: "";
        position: absolute;
        top: 50%;
        left: 0;
        right: 0;
        height: 1px;
        background: rgba(255, 255, 255, 0.1);
        z-index: 1;
      }

      .divider span {
        background: var(--color-dark-grey);
        padding: 0 1rem;
        position: relative;
        z-index: 2;
      }

      .auth-form input {
        width: 100%;
        padding: 1rem;
        margin-bottom: 1rem;
        background: var(--color-black);
        border: 1px solid rgba(255, 255, 255, 0.1);
        border-radius: 8px;
        color: var(--color-white);
        font-family: var(--font-secondary);
      }

      .auth-form input:focus {
        outline: none;
        border-color: var(--color-green);
      }

      .auth-form button[type="submit"] {
        width: 100%;
        margin-top: 1rem;
      }

      #authMessage {
        margin-top: 1rem;
        padding: 1rem;
        border-radius: 8px;
        text-align: center;
        display: none;
      }

      #authMessage.success {
        background: rgba(0, 255, 65, 0.1);
        color: var(--color-green);
        border: 1px solid rgba(0, 255, 65, 0.3);
      }

      #authMessage.error {
        background: rgba(255, 7, 58, 0.1);
        color: var(--color-red);
        border: 1px solid rgba(255, 7, 58, 0.3);
      }

      /* Loading Screen */
      .loading-screen {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: var(--color-black);
        z-index: 2000;
        display: flex;
        align-items: center;
        justify-content: center;
        flex-direction: column;
        opacity: 1;
        visibility: visible;
        transition: all 0.5s ease;
      }

      .loading-screen.hidden {
        opacity: 0;
        visibility: hidden;
      }

      .loader-icon {
        font-size: 4rem;
        color: var(--color-green);
        margin-bottom: 2rem;
        animation: hack-spin 2s infinite linear;
      }

      .loader-text {
        font-family: var(--font-primary);
        font-size: 1.5rem;
        color: var(--color-green);
        animation: typing 2s infinite;
      }

      @keyframes hack-spin {
        0% {
          transform: rotate(0deg) scale(1);
        }
        25% {
          transform: rotate(90deg) scale(1.1);
        }
        50% {
          transform: rotate(180deg) scale(0.9);
        }
        75% {
          transform: rotate(270deg) scale(1.1);
        }
        100% {
          transform: rotate(360deg) scale(1);
        }
      }

      @keyframes typing {
        0%,
        50%,
        100% {
          opacity: 1;
        }
        25%,
        75% {
          opacity: 0.5;
        }
      }

      /* Sidebar */
      .sidebar {
        width: 320px;
        background: var(--color-dark-grey);
        border-right: 1px solid rgba(0, 255, 65, 0.2);
        display: flex;
        flex-direction: column;
        position: fixed;
        height: 100vh;
        z-index: 100;
        overflow-y: auto;
        transition: transform 0.3s ease;
      }

      .sidebar-header {
        padding: 2rem 1.5rem;
        border-bottom: 1px solid rgba(0, 255, 65, 0.2);
        position: sticky;
        top: 0;
        background: var(--color-dark-grey);
        z-index: 10;
      }

      .course-info {
        text-align: center;
      }

      .course-title {
        font-family: var(--font-primary);
        font-size: 1.3rem;
        color: var(--color-green);
        margin-bottom: 0.5rem;
        font-weight: 800;
      }

      .course-progress {
        background: rgba(0, 255, 65, 0.1);
        border: 1px solid rgba(0, 255, 65, 0.3);
        border-radius: 10px;
        padding: 1rem;
        margin-bottom: 1rem;
      }

      .progress-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
        margin-bottom: 0.5rem;
      }

      .progress-label {
        color: var(--color-white);
        font-weight: 600;
        font-size: 0.9rem;
      }

      .progress-percentage {
        color: var(--color-green);
        font-weight: 700;
        font-size: 1rem;
      }

      .progress-bar {
        height: 8px;
        background: rgba(255, 255, 255, 0.1);
        border-radius: 4px;
        overflow: hidden;
        margin-bottom: 0.5rem;
      }

      .progress-fill {
        height: 100%;
        background: linear-gradient(90deg, var(--color-green), #00e63a);
        border-radius: 4px;
        transition: width 0.5s ease;
      }

      .progress-stats {
        display: flex;
        justify-content: space-between;
        font-size: 0.8rem;
        color: #aaa;
      }

      .back-to-dashboard {
        display: flex;
        align-items: center;
        gap: 8px;
        color: var(--color-green);
        text-decoration: none;
        font-size: 0.9rem;
        padding: 8px 12px;
        border: 1px solid rgba(0, 255, 65, 0.3);
        border-radius: 6px;
        transition: all 0.3s ease;
        justify-content: center;
      }

      .back-to-dashboard:hover {
        background: rgba(0, 255, 65, 0.1);
        border-color: var(--color-green);
      }

      /* Lesson Navigation */
      .lesson-nav {
        flex: 1;
        padding: 1rem 0;
      }

      .lesson-item {
        display: flex;
        align-items: center;
        padding: 1rem 1.5rem;
        color: var(--color-white);
        text-decoration: none;
        transition: all 0.3s ease;
        border-left: 3px solid transparent;
        position: relative;
        cursor: pointer;
      }

      .lesson-item:hover {
        background: rgba(0, 255, 65, 0.05);
      }

      .lesson-item.active {
        background: rgba(0, 255, 65, 0.1);
        border-left-color: var(--color-green);
        color: var(--color-green);
      }

      .lesson-item.completed {
        background: rgba(0, 255, 65, 0.05);
        border-left-color: rgba(0, 255, 65, 0.5);
      }

      .lesson-item.locked {
        opacity: 0.4;
        cursor: not-allowed;
        pointer-events: none;
      }

      .lesson-status {
        width: 24px;
        height: 24px;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        margin-right: 1rem;
        font-size: 0.8rem;
        font-weight: 700;
      }

      .lesson-status.not-started {
        background: rgba(255, 255, 255, 0.2);
        color: #aaa;
      }

      .lesson-status.in-progress {
        background: var(--color-orange);
        color: var(--color-black);
      }

      .lesson-status.completed {
        background: var(--color-green);
        color: var(--color-black);
      }

      .lesson-info {
        flex: 1;
      }

      .lesson-title {
        font-weight: 600;
        margin-bottom: 0.2rem;
        font-size: 0.95rem;
      }

      .lesson-meta {
        font-size: 0.75rem;
        color: #aaa;
      }

      .lesson-duration {
        position: absolute;
        right: 1rem;
        top: 50%;
        transform: translateY(-50%);
        font-size: 0.8rem;
        color: #aaa;
      }

      /* Sidebar overlay for mobile */
      .sidebar-overlay {
        display: none;
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: rgba(0, 0, 0, 0.7);
        z-index: 99;
      }

      .sidebar-overlay.active {
        display: block;
      }

      /* Main Content */
      .main-content {
        flex: 1;
        margin-left: 320px;
        display: flex;
        flex-direction: column;
        min-height: 100vh;
      }

      .content-header {
        background: var(--color-dark-grey);
        border-bottom: 1px solid rgba(0, 255, 65, 0.2);
        padding: 1.5rem 2rem;
        position: sticky;
        top: 0;
        z-index: 50;
      }

      .lesson-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
        flex-wrap: wrap;
        gap: 1rem;
      }

      .lesson-header-left {
        display: flex;
        align-items: center;
        gap: 1rem;
        flex-wrap: wrap;
      }

      .lesson-number {
        background: var(--color-green);
        color: var(--color-black);
        padding: 0.5rem 1rem;
        border-radius: 20px;
        font-weight: 700;
        font-size: 0.9rem;
      }

      .lesson-header-title {
        font-family: var(--font-primary);
        font-size: 1.5rem;
        color: var(--color-white);
        font-weight: 800;
        max-width: 100%;
        overflow: hidden;
        text-overflow: ellipsis;
      }

      .lesson-actions {
        display: flex;
        gap: 1rem;
        align-items: center;
      }

      .btn-primary {
        background: var(--color-green);
        color: var(--color-black);
      }

      .btn-primary:hover {
        background: #00e63a;
      }

      .btn:disabled {
        opacity: 0.5;
        cursor: not-allowed;
      }

      /* Content Body */
      .content-body {
        flex: 1;
        padding: 2rem;
        overflow-y: auto;
      }

      .lesson-content {
        max-width: 900px;
        margin: 0 auto;
      }

      .content-section {
        margin-bottom: 3rem;
      }

      .content-section h2 {
        font-family: var(--font-primary);
        font-size: 1.8rem;
        color: var(--color-green);
        margin-bottom: 1rem;
        font-weight: 800;
      }

      .content-section h3 {
        font-family: var(--font-primary);
        font-size: 1.4rem;
        color: var(--color-white);
        margin: 2rem 0 1rem 0;
        font-weight: 700;
      }

      .content-section p {
        line-height: 1.7;
        margin-bottom: 1.2rem;
        color: #ddd;
        font-size: 1rem;
      }

      .content-section ul,
      .content-section ol {
        margin: 1rem 0 1.5rem 2rem;
      }

      .content-section li {
        margin-bottom: 0.5rem;
        color: #ddd;
        line-height: 1.6;
      }

      .content-image {
        max-width: 100%;
        height: auto;
        border-radius: 10px;
        margin: 2rem 0;
        border: 2px solid rgba(0, 255, 65, 0.3);
      }

      /* Code Blocks */
      .code-section {
        margin: 2rem 0;
      }

      .code-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
        background: #1e1e1e;
        padding: 1rem 1.5rem;
        border-radius: 10px 10px 0 0;
        border: 1px solid rgba(0, 255, 65, 0.3);
      }

      .code-title {
        color: var(--color-green);
        font-weight: 600;
        font-size: 0.9rem;
      }

      .copy-btn {
        background: rgba(0, 255, 65, 0.1);
        border: 1px solid rgba(0, 255, 65, 0.3);
        color: var(--color-green);
        padding: 0.5rem 1rem;
        border-radius: 4px;
        cursor: pointer;
        font-size: 0.8rem;
        transition: all 0.3s ease;
      }

      .copy-btn:hover {
        background: rgba(0, 255, 65, 0.2);
      }

      .code-block {
        background: #1e1e1e !important;
        margin: 0 !important;
        padding: 1.5rem !important;
        border-radius: 0 0 10px 10px !important;
        border: 1px solid rgba(0, 255, 65, 0.3);
        border-top: none;
        font-size: 0.9rem;
        line-height: 1.5;
        overflow-x: auto;
      }

      /* Info Boxes */
      .info-box {
        padding: 1.5rem;
        border-radius: 10px;
        margin: 2rem 0;
        border-left: 4px solid;
      }

      .info-box.note {
        background: rgba(0, 191, 255, 0.1);
        border-left-color: var(--color-blue);
        border: 1px solid rgba(0, 191, 255, 0.3);
      }

      .info-box.warning {
        background: rgba(255, 140, 0, 0.1);
        border-left-color: var(--color-orange);
        border: 1px solid rgba(255, 140, 0, 0.3);
      }

      .info-box.danger {
        background: rgba(255, 7, 58, 0.1);
        border-left-color: var(--color-red);
        border: 1px solid rgba(255, 7, 58, 0.3);
      }

      .info-box.tip {
        background: rgba(0, 255, 65, 0.1);
        border-left-color: var(--color-green);
        border: 1px solid rgba(0, 255, 65, 0.3);
      }

      .info-box-header {
        display: flex;
        align-items: center;
        gap: 0.5rem;
        margin-bottom: 1rem;
        font-weight: 700;
      }

      .info-box.note .info-box-header {
        color: var(--color-blue);
      }

      .info-box.warning .info-box-header {
        color: var(--color-orange);
      }

      .info-box.danger .info-box-header {
        color: var(--color-red);
      }

      .info-box.tip .info-box-header {
        color: var(--color-green);
      }

      /* Quiz Section */
      .quiz-section {
        background: var(--color-dark-grey);
        border: 2px solid rgba(0, 255, 65, 0.3);
        border-radius: 15px;
        padding: 2rem;
        margin: 3rem 0;
      }

      .quiz-header {
        text-align: center;
        margin-bottom: 2rem;
      }

      .quiz-title {
        font-family: var(--font-primary);
        font-size: 1.8rem;
        color: var(--color-green);
        margin-bottom: 1rem;
        font-weight: 800;
      }

      .quiz-info {
        color: #aaa;
        font-size: 0.9rem;
      }

      .quiz-question {
        margin-bottom: 2rem;
        display: none;
      }

      .quiz-question.active {
        display: block;
      }

      .question-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
        margin-bottom: 1.5rem;
        position: relative;
      }

      .question-number {
        background: var(--color-green);
        color: var(--color-black);
        padding: 0.5rem 1rem;
        border-radius: 20px;
        font-weight: 700;
        font-size: 0.9rem;
      }

      .question-progress {
        color: #aaa;
        font-size: 0.9rem;
      }

      .question-text {
        font-size: 1.1rem;
        color: var(--color-white);
        margin-bottom: 1.5rem;
        font-weight: 600;
        line-height: 1.5;
      }

      .question-options {
        display: flex;
        flex-direction: column;
        gap: 1rem;
      }

      .option {
        background: rgba(255, 255, 255, 0.05);
        border: 2px solid rgba(255, 255, 255, 0.1);
        border-radius: 10px;
        padding: 1rem 1.5rem;
        cursor: pointer;
        transition: all 0.3s ease;
        display: flex;
        align-items: center;
        gap: 1rem;
      }

      .option:hover {
        background: rgba(0, 255, 65, 0.1);
        border-color: rgba(0, 255, 65, 0.3);
      }

      .option.selected {
        background: rgba(0, 255, 65, 0.2);
        border-color: var(--color-green);
        color: var(--color-green);
      }

      .option.correct {
        background: rgba(0, 255, 65, 0.2);
        border-color: var(--color-green);
        color: var(--color-green);
      }

      .option.incorrect {
        background: rgba(255, 7, 58, 0.2);
        border-color: var(--color-red);
        color: var(--color-red);
      }

      .option-letter {
        width: 30px;
        height: 30px;
        border-radius: 50%;
        background: rgba(255, 255, 255, 0.1);
        display: flex;
        align-items: center;
        justify-content: center;
        font-weight: 700;
        font-size: 0.9rem;
      }

      .option.selected .option-letter {
        background: var(--color-green);
        color: var(--color-black);
      }

      .quiz-controls {
        display: flex;
        justify-content: space-between;
        align-items: center;
        margin-top: 2rem;
        padding-top: 1.5rem;
        border-top: 1px solid rgba(255, 255, 255, 0.1);
      }

      .quiz-results {
        text-align: center;
        padding: 2rem;
        display: none;
      }

      .quiz-results.show {
        display: block;
      }

      .quiz-score {
        font-family: var(--font-primary);
        font-size: 3rem;
        font-weight: 900;
        margin-bottom: 1rem;
      }

      .quiz-score.pass {
        color: var(--color-green);
      }

      .quiz-score.fail {
        color: var(--color-red);
      }

      .quiz-message {
        font-size: 1.2rem;
        margin-bottom: 2rem;
        line-height: 1.5;
      }

      .quiz-actions {
        display: flex;
        gap: 1rem;
        justify-content: center;
      }

      /* Achievement Notification */
      .achievement-notification {
        position: fixed;
        top: 20px;
        right: 20px;
        background: linear-gradient(
          135deg,
          var(--color-dark-grey),
          var(--color-black)
        );
        border: 2px solid var(--color-gold);
        border-radius: 12px;
        padding: 1.5rem;
        max-width: 400px;
        z-index: 3000;
        transform: translateX(400px);
        opacity: 0;
        transition: all 0.5s ease;
        box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
      }

      .achievement-notification.show {
        transform: translateX(0);
        opacity: 1;
      }

      .notification-header {
        display: flex;
        align-items: center;
        gap: 1rem;
        margin-bottom: 1rem;
      }

      .notification-icon {
        font-size: 2rem;
        width: 50px;
        height: 50px;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        background: radial-gradient(var(--color-gold), #b8860b);
        color: var(--color-black);
      }

      .notification-content h3 {
        color: var(--color-gold);
        font-family: var(--font-primary);
        font-size: 1.1rem;
        margin: 0;
      }

      .notification-content p {
        color: var(--color-white);
        font-size: 0.9rem;
        margin: 0.3rem 0 0 0;
      }

      .notification-reward {
        background: rgba(0, 255, 65, 0.1);
        border: 1px solid var(--color-green);
        border-radius: 6px;
        padding: 0.5rem;
        margin-top: 0.8rem;
        display: flex;
        align-items: center;
        gap: 0.5rem;
        font-size: 0.8rem;
        color: var(--color-green);
      }

      /* Toast Notifications */
      .toast {
        position: fixed;
        top: 20px;
        left: 50%;
        transform: translateX(-50%);
        background: var(--color-dark-grey);
        border: 1px solid var(--color-green);
        border-radius: 8px;
        padding: 1rem 1.5rem;
        color: var(--color-white);
        z-index: 2000;
        opacity: 0;
        visibility: hidden;
        transition: all 0.3s ease;
      }

      .toast.show {
        opacity: 1;
        visibility: visible;
      }

      .toast.success {
        border-color: var(--color-green);
      }

      .toast.error {
        border-color: var(--color-red);
      }

      .toast.warning {
        border-color: var(--color-orange);
      }

      /* Navigation Controls */
      .lesson-navigation {
        background: var(--color-dark-grey);
        border-top: 1px solid rgba(0, 255, 65, 0.2);
        padding: 1.5rem 2rem;
        display: flex;
        justify-content: space-between;
        align-items: center;
      }

      .nav-info {
        color: #aaa;
        font-size: 0.9rem;
      }

      .nav-controls {
        display: flex;
        gap: 1rem;
      }

      /* Responsive Design */
      @media (max-width: 1200px) {
        .sidebar {
          width: 280px;
        }

        .main-content {
          margin-left: 280px;
        }
      }

      @media (max-width: 992px) {
        .content-header {
          padding: 1rem;
        }

        .content-body {
          padding: 1rem;
        }

        .lesson-navigation {
          padding: 1rem;
        }
      }

      @media (max-width: 768px) {
        .sidebar {
          transform: translateX(-100%);
          width: 280px;
        }

        .sidebar.open {
          transform: translateX(0);
          box-shadow: 5px 0 15px rgba(0, 0, 0, 0.5);
        }

        .main-content {
          margin-left: 0;
          width: 100%;
        }

        .lesson-header {
          flex-direction: column;
          align-items: flex-start;
        }

        .lesson-actions {
          width: 100%;
          justify-content: space-between;
          flex-wrap: wrap;
          gap: 0.5rem;
        }

        .content-section h2 {
          font-size: 1.5rem;
        }

        .content-section h3 {
          font-size: 1.2rem;
        }

        .quiz-section {
          padding: 1rem;
        }

        .quiz-controls {
          flex-direction: column;
          gap: 1rem;
        }

        .quiz-actions {
          flex-direction: column;
        }

        .lesson-navigation {
          flex-direction: column;
          gap: 1rem;
        }

        .nav-controls {
          width: 100%;
          justify-content: space-between;
        }

        .code-header {
          flex-direction: column;
          gap: 0.5rem;
          align-items: flex-start;
        }

        .info-box {
          padding: 1rem;
        }
      }

      @media (max-width: 576px) {
        .modal-content {
          padding: 1.5rem;
        }

        .auth-tab {
          padding: 0.75rem;
          font-size: 0.9rem;
        }

        .lesson-header-title {
          font-size: 1.2rem;
        }

        .content-section h2 {
          font-size: 1.3rem;
        }

        .quiz-title {
          font-size: 1.4rem;
        }

        .option {
          padding: 0.75rem 1rem;
        }

        .quiz-score {
          font-size: 2.5rem;
        }

        .btn {
          padding: 8px 16px;
          font-size: 0.85rem;
        }
      }

      /* Custom Scrollbar */
      ::-webkit-scrollbar {
        width: 8px;
      }

      ::-webkit-scrollbar-track {
        background: var(--color-dark-grey);
      }

      ::-webkit-scrollbar-thumb {
        background: var(--color-green);
        border-radius: 4px;
      }

      ::-webkit-scrollbar-thumb:hover {
        background: #00e63a;
      }

      /* Animation Classes */
      .fade-in {
        animation: fadeIn 0.5s ease-in;
      }

      @keyframes fadeIn {
        from {
          opacity: 0;
          transform: translateY(20px);
        }
        to {
          opacity: 1;
          transform: translateY(0);
        }
      }

      .slide-in-right {
        animation: slideInRight 0.5s ease-out;
      }

      @keyframes slideInRight {
        from {
          transform: translateX(100%);
          opacity: 0;
        }
        to {
          transform: translateX(0);
          opacity: 1;
        }
      }

      /* Loading states */
      .loading {
        opacity: 0.6;
        pointer-events: none;
      }

      .spinner {
        width: 20px;
        height: 20px;
        border: 2px solid rgba(0, 255, 65, 0.3);
        border-top: 2px solid var(--color-green);
        border-radius: 50%;
        animation: spin 1s linear infinite;
      }

      @keyframes spin {
        0% {
          transform: rotate(0deg);
        }
        100% {
          transform: rotate(360deg);
        }
      }
      /* Base Mobile-First Styles */
      @media (max-width: 768px) {
        /* Header controls completely redesigned for mobile */
        .header-controls {
          position: fixed;
          top: 8px;
          right: 8px;
          left: 8px;
          z-index: 10000;
          display: flex;
          flex-direction: row;
          gap: 6px;
          padding: 0;
          height: auto;
          background: transparent;
        }

        /* Music dropdown mobile optimization */
        .music-dropdown {
          flex: 1;
          min-width: 0;
        }

        .music-dropdown button {
          width: 100%;
          padding: 8px 10px;
          font-size: 0.75rem;
          border-radius: 4px;
          white-space: nowrap;
          overflow: hidden;
          text-overflow: ellipsis;
        }

        #music-button-text {
          display: none;
        }

        #music-icon {
          font-size: 1rem;
        }

        .music-dropdown-content {
          position: fixed;
          top: 50px;
          left: 8px;
          right: 8px;
          width: auto;
          min-width: auto;
          max-height: 50vh;
          overflow-y: auto;
          box-shadow: 0 4px 20px rgba(0, 0, 0, 0.5);
        }

        /* Reset button mobile */
        #resetProgressBtn {
          padding: 8px 10px;
          font-size: 0.75rem;
          border-radius: 4px;
          min-width: 80px;
          flex-shrink: 0;
        }

        #resetProgressBtn span {
          display: none;
        }

        /* Sidebar completely mobile optimized */
        .sidebar {
          height: 100vh;
          position: fixed;
          top: 0;
          left: 0;
          transform: translateX(-100%);
          z-index: 1000;
          overflow-y: auto;
          transition: transform 0.3s ease;
        }

        .sidebar.open {
          transform: translateX(0);
        }

        .sidebar-header {
          padding: 60px 1rem 1.5rem 1rem;
          position: sticky;
          top: 0;
          background: var(--color-dark-grey);
          z-index: 10;
        }

        .course-title {
          font-size: 1.1rem;
          margin-bottom: 0.5rem;
        }

        .course-progress {
          padding: 0.8rem;
          margin-bottom: 0.8rem;
        }

        .progress-label,
        .progress-percentage {
          font-size: 0.8rem;
        }

        /* Lesson navigation mobile */
        .lesson-item {
          padding: 0.75rem 1rem;
          min-height: 60px;
          display: flex;
          align-items: center;
        }

        .lesson-title {
          font-size: 0.85rem;
          line-height: 1.3;
        }

        .lesson-meta {
          font-size: 0.7rem;
        }

        .lesson-duration {
          font-size: 0.7rem;
          position: relative;
          right: 0;
          transform: none;
        }

        /* Main content mobile */
        .main-content {
          margin-left: 0;
          width: 100%;
          padding-top: 50px;
        }

        /* Content header mobile */
        .content-header {
          padding: 0.75rem 1rem;
          position: fixed;
          top: 50px;
          left: 0;
          right: 0;
          z-index: 100;
          background: var(--color-dark-grey);
        }

        .lesson-header {
          flex-direction: column;
          align-items: flex-start;
          gap: 0.75rem;
        }

        .lesson-header-left {
          width: 100%;
          flex-wrap: wrap;
          gap: 0.5rem;
        }

        .lesson-number {
          padding: 0.3rem 0.8rem;
          font-size: 0.8rem;
        }

        .lesson-header-title {
          font-size: 1.1rem;
          line-height: 1.3;
          max-width: 100%;
          word-break: break-word;
        }

        .lesson-actions {
          width: 100%;
          justify-content: space-between;
        }

        #menuToggle {
          padding: 8px 12px;
          font-size: 0.8rem;
        }

        /* Content body mobile */
        .content-body {
          padding: 1rem 0.75rem;
          margin-top: 120px;
          margin-bottom: 80px;
          overflow-y: auto;
          -webkit-overflow-scrolling: touch;
        }

        .lesson-content {
          max-width: 100%;
          margin: 0;
          padding: 0;
        }

        /* Content sections mobile */
        .content-section {
          margin-bottom: 2rem;
        }

        .content-section h2 {
          font-size: 1.3rem;
          margin-bottom: 0.8rem;
          line-height: 1.3;
          word-break: break-word;
        }

        .content-section h3 {
          font-size: 1.1rem;
          margin: 1.5rem 0 0.8rem 0;
          line-height: 1.3;
        }

        .content-section p {
          font-size: 0.9rem;
          line-height: 1.6;
          margin-bottom: 1rem;
        }

        .content-section ul,
        .content-section ol {
          margin: 0.8rem 0 1.2rem 1.5rem;
          font-size: 0.9rem;
        }

        .content-section li {
          margin-bottom: 0.4rem;
          line-height: 1.5;
        }

        /* Code sections mobile */
        .code-section {
          margin: 1.5rem -0.75rem;
        }

        .code-header {
          padding: 0.75rem 1rem;
          flex-direction: column;
          gap: 0.5rem;
          align-items: flex-start;
        }

        .code-title {
          font-size: 0.8rem;
        }

        .copy-btn {
          padding: 0.4rem 0.8rem;
          font-size: 0.75rem;
          align-self: flex-end;
        }

        .code-block {
          padding: 1rem !important;
          font-size: 0.8rem !important;
          line-height: 1.4 !important;
          overflow-x: auto;
          white-space: pre;
          -webkit-overflow-scrolling: touch;
        }

        /* Info boxes mobile */
        .info-box {
          padding: 1rem 0.75rem;
          margin: 1.5rem -0.75rem;
          border-radius: 6px;
        }

        .info-box-header {
          font-size: 0.9rem;
          margin-bottom: 0.8rem;
        }

        .info-box p {
          font-size: 0.85rem;
          line-height: 1.5;
        }

        /* Quiz section mobile */
        .quiz-section {
          padding: 1rem 0.75rem;
          margin: 2rem -0.75rem;
          border-radius: 8px;
        }

        .quiz-header {
          text-align: center;
          margin-bottom: 1.5rem;
        }

        .quiz-title {
          font-size: 1.4rem;
          margin-bottom: 0.8rem;
          line-height: 1.3;
        }

        .quiz-info {
          font-size: 0.85rem;
        }

        /* Quiz questions mobile */
        .question-header {
          flex-direction: column;
          align-items: flex-start;
          gap: 0.5rem;
          margin-bottom: 1rem;
        }

        .question-number {
          padding: 0.4rem 0.8rem;
          font-size: 0.8rem;
        }

        .question-progress {
          font-size: 0.8rem;
          align-self: flex-end;
        }

        .question-text {
          font-size: 1rem;
          line-height: 1.4;
          margin-bottom: 1.2rem;
        }

        .question-options {
          gap: 0.8rem;
        }

        .option {
          padding: 0.75rem 1rem;
          border-radius: 8px;
          font-size: 0.9rem;
        }

        .option-letter {
          width: 28px;
          height: 28px;
          font-size: 0.8rem;
        }

        /* Quiz controls mobile */
        .quiz-controls {
          flex-direction: column;
          gap: 1rem;
          margin-top: 1.5rem;
          padding-top: 1.2rem;
        }

        .quiz-controls > div {
          display: flex;
          gap: 0.8rem;
          width: 100%;
        }

        .quiz-controls .btn {
          flex: 1;
          padding: 0.75rem 1rem;
          font-size: 0.85rem;
        }

        /* Quiz results mobile */
        .quiz-results {
          padding: 1.5rem 0;
        }

        .quiz-score {
          font-size: 2.5rem;
          margin-bottom: 1rem;
        }

        .quiz-message {
          font-size: 1rem;
          line-height: 1.4;
          margin-bottom: 1.5rem;
        }

        .quiz-actions {
          flex-direction: column;
          gap: 0.8rem;
        }

        .quiz-actions .btn {
          width: 100%;
          padding: 0.75rem;
        }

        /* Navigation footer mobile */
        .lesson-navigation {
          position: fixed;
          bottom: 0;
          left: 0;
          right: 0;
          padding: 0.75rem 1rem;
          background: var(--color-dark-grey);
          border-top: 1px solid rgba(0, 255, 65, 0.2);
          z-index: 50;
        }

        .nav-info {
          font-size: 0.8rem;
          text-align: center;
          margin-bottom: 0.5rem;
        }

        .nav-controls {
          width: 100%;
          justify-content: space-between;
          gap: 0.8rem;
        }

        .nav-controls .btn {
          flex: 1;
          padding: 0.75rem 1rem;
          font-size: 0.85rem;
          max-width: 48%;
        }

        /* Achievement notification mobile */
        .achievement-notification {
          top: 60px;
          left: 8px;
          right: 8px;
          max-width: none;
          padding: 1rem;
          border-radius: 8px;
        }

        .notification-header {
          gap: 0.75rem;
          margin-bottom: 0.8rem;
        }

        .notification-icon {
          width: 40px;
          height: 40px;
          font-size: 1.5rem;
        }

        .notification-content h3 {
          font-size: 1rem;
          margin: 0;
        }

        .notification-content p {
          font-size: 0.8rem;
          margin: 0.3rem 0 0 0;
        }

        .notification-reward {
          padding: 0.4rem;
          margin-top: 0.6rem;
          font-size: 0.75rem;
        }

        /* Toast mobile */
        .toast {
          top: 60px;
          left: 8px;
          right: 8px;
          transform: none;
          padding: 0.75rem 1rem;
          border-radius: 6px;
          font-size: 0.9rem;
        }

        /* Auth modal mobile */
        .modal-content {
          margin: 0 8px;
          padding: 1.5rem;
          max-width: none;
          width: auto;
          border-radius: 12px;
        }

        .auth-tab {
          padding: 0.75rem 0.5rem;
          font-size: 0.9rem;
        }

        .auth-form h2 {
          font-size: 1.3rem;
          margin-bottom: 1.5rem;
        }

        .auth-form input {
          padding: 0.75rem;
          font-size: 0.9rem;
        }

        /* Loading screen mobile */
        .loader-icon {
          font-size: 3rem;
          margin-bottom: 1.5rem;
        }

        .loader-text {
          font-size: 1.2rem;
          text-align: center;
          padding: 0 1rem;
        }

        /* Utility classes for mobile */
        .mobile-hidden {
          display: none !important;
        }

        .mobile-full-width {
          width: 100% !important;
        }

        .mobile-text-center {
          text-align: center !important;
        }

        /* Touch optimization */
        .btn,
        .option,
        .lesson-item {
          -webkit-tap-highlight-color: transparent;
          touch-action: manipulation;
        }

        /* Prevent zoom on input focus */
        input,
        select,
        textarea {
          font-size: 16px !important;
        }

        /* Safe area handling for notched devices */
        .header-controls {
          padding-top: env(safe-area-inset-top, 8px);
        }

        .content-header {
          top: calc(50px + env(safe-area-inset-top, 0px));
        }

        .content-body {
          margin-top: calc(120px + env(safe-area-inset-top, 0px));
          margin-bottom: calc(80px + env(safe-area-inset-bottom, 0px));
        }

        .lesson-navigation {
          bottom: env(safe-area-inset-bottom, 0px);
          padding-bottom: calc(0.75rem + env(safe-area-inset-bottom, 0px));
        }
      }

      /* Extra small devices (phones < 576px) */
      @media (max-width: 575px) {
        .header-controls {
          gap: 4px;
        }

        #resetProgressBtn {
          min-width: 70px;
          padding: 8px;
        }

        .content-header {
          padding: 0.5rem 0.75rem;
        }

        .lesson-header-title {
          font-size: 1rem;
        }

        .content-body {
          padding: 0.75rem 0.5rem;
        }

        .content-section h2 {
          font-size: 1.2rem;
        }

        .content-section h3 {
          font-size: 1rem;
        }

        .quiz-title {
          font-size: 1.2rem;
        }

        .quiz-score {
          font-size: 2rem;
        }
      }

      /* Landscape orientation fixes */
      @media (max-width: 768px) and (orientation: landscape) {
        .content-body {
          margin-top: 100px;
        }

        .sidebar-header {
          padding-top: 1.5rem;
        }
      }
      /* ---------- Mobile header overlap fix ---------- */
      .mbtn {
        border-radius: 8px;
        gap: 2px;
      }