:root {
      --primary: #3898ec;
      --primary-light: #5baee7;
      --accent: #ff1654;
      --accent-light: #ff4d7d;
      --success: #4ded9f;
      --warning: #ffb347;
      --dark-bg: #1a1a1a;
      --dark-bg2: #242424;
      --dark-bg3: #2d2d2d;
      --text-light: #e8e8e8;
      --text-muted: #a0a0a0;
      --border-color: #3a3a3a;
      --sidebar-width: 280px;
      --header-height: 60px;
    }

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

    body {
      font-family: 'Poppins', sans-serif;
      background: var(--dark-bg);
      color: var(--text-light);
      overflow: hidden;
      height: 100vh;
    }

    /* HEADER */
    header {
      height: var(--header-height);
      background: var(--dark-bg2);
      border-bottom: 1px solid var(--border-color);
      display: flex;
      align-items: center;
      padding: 0 32px;
      gap: 20px;
      position: relative;
      z-index: 100;
    }

    .logo {
      font-size: 22px;
      font-weight: 800;
      letter-spacing: -0.5px;
      color: var(--text-light);
    }

    .logo span {
      color: var(--primary);
    }

    .header-divider {
      width: 1px;
      height: 24px;
      background: var(--border-color);
    }

    .breadcrumb {
      font-size: 12px;
      color: var(--text-muted);
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .header-right {
      margin-left: auto;
      display: flex;
      align-items: center;
      gap: 20px;
    }

    .progress-info {
      display: flex;
      align-items: center;
      gap: 10px;
    }

    .progress-text {
      font-size: 12px;
      color: var(--text-muted);
    }

    .progress-bar {
      width: 140px;
      height: 3px;
      background: var(--dark-bg3);
      border-radius: 2px;
      overflow: hidden;
    }

    .progress-fill {
      height: 100%;
      background: linear-gradient(90deg, var(--primary), var(--accent-light));
      width: 0%;
      transition: width 0.4s ease;
    }

    .home-btn {
      font-size: 12px;
      padding: 8px 16px;
      background: transparent;
      border: 1px solid var(--border-color);
      color: var(--text-light);
      border-radius: 4px;
      cursor: pointer;
      transition: all 0.2s;
      text-decoration: none;
    }

    .home-btn:hover {
      border-color: var(--primary);
      color: var(--primary);
    }

    /* CONTAINER */
    .container {
      display: flex;
      height: calc(100vh - var(--header-height));
      overflow: hidden;
    }

    /* SIDEBAR */
    aside {
      width: var(--sidebar-width);
      background: var(--dark-bg2);
      border-right: 1px solid var(--border-color);
      display: flex;
      flex-direction: column;
      overflow-y: auto;
      flex-shrink: 0;
    }

    .sidebar-section {
      padding: 16px;
      border-bottom: 1px solid var(--border-color);
    }

    .sidebar-title {
      font-size: 10px;
      font-weight: 700;
      letter-spacing: 1px;
      text-transform: uppercase;
      color: var(--text-muted);
      margin-bottom: 12px;
    }

    .module-item {
      padding: 12px 16px;
      margin-bottom: 6px;
      border-left: 3px solid transparent;
      cursor: pointer;
      border-radius: 4px;
      transition: all 0.2s;
      font-size: 13px;
      font-weight: 500;
      color: var(--text-muted);
    }

    .module-item:hover {
      background: var(--dark-bg3);
      color: var(--text-light);
    }

    .module-item.active {
      background: rgba(56, 152, 236, 0.15);
      border-left-color: var(--primary);
      color: var(--primary);
    }

    .lesson-sub {
      padding: 8px 16px 8px 32px;
      margin-bottom: 4px;
      font-size: 12px;
      color: var(--text-muted);
      cursor: pointer;
      border-radius: 4px;
      transition: all 0.2s;
    }

    .lesson-sub:hover {
      background: var(--dark-bg3);
      color: var(--text-light);
    }

    .lesson-sub.active {
      color: var(--success);
      font-weight: 600;
    }

    /* MAIN CONTENT */
    main {
      flex: 1;
      display: flex;
      flex-direction: column;
      overflow: hidden;
    }

    .content-area {
      flex: 1;
      display: flex;
      flex-direction: column;
      overflow-y: auto;
      padding: 32px 40px;
    }

    .lesson-header {
      margin-bottom: 24px;
    }

    .lesson-tag {
      font-size: 11px;
      font-weight: 700;
      letter-spacing: 1px;
      text-transform: uppercase;
      color: var(--primary);
      margin-bottom: 8px;
    }

    .lesson-title {
      font-size: 32px;
      font-weight: 800;
      color: var(--text-light);
      margin-bottom: 8px;
      letter-spacing: -0.5px;
    }

    .lesson-subtitle {
      font-size: 14px;
      color: var(--text-muted);
      font-weight: 300;
    }

    .section {
      margin-bottom: 32px;
    }

    .section-title {
      font-size: 18px;
      font-weight: 700;
      color: var(--text-light);
      margin-bottom: 12px;
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .section-title::before {
      content: '';
      width: 4px;
      height: 4px;
      background: var(--primary);
      border-radius: 50%;
    }

    .content-text {
      font-size: 14px;
      line-height: 1.8;
      color: var(--text-light);
      margin-bottom: 16px;
    }

    /* CODE BLOCKS */
    .code-block {
      background: var(--dark-bg3);
      border: 1px solid var(--border-color);
      border-left: 3px solid var(--primary);
      border-radius: 6px;
      padding: 16px;
      margin: 16px 0;
      font-family: 'JetBrains Mono', monospace;
      font-size: 13px;
      color: #a8d4ff;
      line-height: 1.6;
      overflow-x: auto;
    }

    .code-block code {
      color: inherit;
    }

    .kw { color: #ff79c6; font-weight: 600; }
    .str { color: #f1fa8c; }
    .num { color: #bd93f9; }
    .com { color: #6272a4; }

    /* INTERACTIVE ELEMENTS */
    .interactive-box {
      background: rgba(56, 152, 236, 0.08);
      border: 1px solid rgba(56, 152, 236, 0.3);
      border-radius: 8px;
      padding: 20px;
      margin: 16px 0;
    }

    .interactive-title {
      font-size: 14px;
      font-weight: 700;
      color: var(--primary);
      margin-bottom: 12px;
    }

    .input-group {
      display: flex;
      gap: 12px;
      margin-bottom: 12px;
      flex-wrap: wrap;
    }

    .input-field {
      display: flex;
      flex-direction: column;
      gap: 6px;
    }

    .input-field label {
      font-size: 12px;
      font-weight: 600;
      color: var(--text-muted);
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .input-field input {
      padding: 10px 14px;
      background: var(--dark-bg2);
      border: 1px solid var(--border-color);
      border-radius: 4px;
      color: var(--text-light);
      font-family: 'JetBrains Mono', monospace;
      font-size: 13px;
      transition: border-color 0.2s;
    }

    .input-field input:focus {
      outline: none;
      border-color: var(--primary);
    }

    .button {
      padding: 10px 20px;
      background: var(--primary);
      border: none;
      border-radius: 4px;
      color: white;
      font-weight: 600;
      cursor: pointer;
      transition: all 0.2s;
      font-size: 13px;
      font-family: 'Poppins', sans-serif;
    }

    .button:hover {
      background: var(--primary-light);
      transform: translateY(-2px);
      box-shadow: 0 4px 12px rgba(56, 152, 236, 0.3);
    }

    .result-box {
      background: var(--dark-bg2);
      border: 1px solid var(--border-color);
      border-radius: 6px;
      padding: 16px;
      margin-top: 12px;
      display: none;
    }

    .result-box.visible {
      display: block;
    }

    .result-label {
      font-size: 11px;
      font-weight: 700;
      letter-spacing: 1px;
      text-transform: uppercase;
      color: var(--text-muted);
      margin-bottom: 8px;
    }

    .result-value {
      font-family: 'JetBrains Mono', monospace;
      font-size: 18px;
      font-weight: 700;
      color: var(--success);
    }

    /* LIST STYLES */
    ul {
      margin: 16px 0;
      padding-left: 20px;
    }

    li {
      margin-bottom: 8px;
      line-height: 1.6;
    }

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

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

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

    ::-webkit-scrollbar-thumb:hover {
      background: var(--text-muted);
    }

    /* RESPONSIVE */
    @media (max-width: 768px) {
      aside {
        width: 240px;
      }

      .content-area {
        padding: 20px;
      }

      .lesson-title {
        font-size: 24px;
      }

      header {
        padding: 0 16px;
      }
    }