:root {
      --primary: #2c3e50;
      --accent: #e67e22;
      --accent-hover: #d35400;
      --bg: #f8f9fa;
      --card-bg: #ffffff;
    }

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

    body {
      font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
      background: var(--bg);
      color: var(--primary);
      line-height: 1.6;
    }

    /* Header */
    header {
      text-align: center;
      padding: 3rem 1rem;
      background: linear-gradient(135deg, #2c3e50 0%, #34495e 100%);
      color: white;
      border-bottom: 5px solid var(--accent);
    }

    header h1 {
      font-size: 3.5rem;
      margin-bottom: 0.5rem;
      letter-spacing: 1px;
    }

    header p {
      font-size: 1.5rem;
      opacity: 0.9;
      max-width: 600px;
      margin: 0 auto;
    }

    .container {
      max-width: 1100px;
      margin: 0 auto;
      padding: 2rem 1rem;
    }

    /* Felsefe Kutusu */
    .intro {
      text-align: center;
      margin-bottom: 2rem;
      padding: 1rem;
    }

    .intro h2 {
      font-size: 1.5rem;
      color: var(--accent);
      margin-bottom: 0.5rem;
    }

    /* ===== YENİ: Arama ve Kategori Alanı ===== */
    .filter-panel {
      max-width: 900px;
      margin: 0 auto 3rem auto;
      padding: 0 1rem;
    }

    .search-box {
      width: 100%;
      padding: 14px 20px;
      margin-bottom: 1.2rem;
      border: 2px solid #ecf0f1;
      border-radius: 50px;
      font-size: 1rem;
      background: white;
      color: var(--primary);
      outline: none;
      transition: all 0.3s ease;
      box-shadow: 0 2px 8px rgba(0,0,0,0.04);
    }

    .search-box:focus {
      border-color: var(--accent);
      box-shadow: 0 4px 15px rgba(230, 126, 34, 0.15);
    }

    .categories {
      display: flex;
      flex-wrap: wrap;
      gap: 10px;
      justify-content: center;
    }

    .cat-btn {
      padding: 8px 20px;
      border: 2px solid #ecf0f1;
      background: white;
      border-radius: 50px;
      cursor: pointer;
      font-size: 0.9rem;
      color: var(--primary);
      font-weight: 600;
      transition: all 0.25s ease;
      box-shadow: 0 2px 6px rgba(0,0,0,0.04);
    }

    .cat-btn:hover {
      transform: translateY(-2px);
      border-color: var(--accent);
      color: var(--accent);
    }

    .cat-btn.active {
      background: var(--accent);
      color: white;
      border-color: var(--accent);
      box-shadow: 0 4px 12px rgba(230, 126, 34, 0.35);
    }

    .no-results {
      text-align: center;
      padding: 2rem;
      color: #7f8c8d;
      font-size: 1rem;
      background: white;
      border-radius: 16px;
      border: 2px dashed #ecf0f1;
      display: none;
      max-width: 500px;
      margin: 0 auto;
    }
    /* ===== YENİ Alan Sonu ===== */

    /* Ana Akış Alanı (Dikey) */
    .flow-container {
      position: relative;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 2rem;
    }

    /* Üst Kısım: 7 Temel Ders (Grid) */
    .source-nodes {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
      gap: 2rem;
      width: 100%;
      max-width: 900px;
      position: relative;
      z-index: 2;
    }

    .node-link {
      text-decoration: none;
      color: inherit;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      transition: transform 0.3s ease, opacity 0.3s ease;
    }

    .node-link:hover {
      transform: translateY(-5px);
    }

    /* Filtreleme sırasında gizlenen daireler için */
    .node-link.hidden {
      display: none;
    }

    /* Büyük Daireler */
    .big-circle {
      width: 140px;
      height: 140px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 3.5rem;
      background: white;
      box-shadow: 0 8px 25px rgba(0,0,0,0.1);
      border: 4px solid white;
      margin-bottom: 1rem;
      transition: all 0.3s ease;
      position: relative;
      overflow: hidden;
    }

    .node-link:hover .big-circle {
      transform: scale(1.08);
      box-shadow: 0 12px 30px rgba(0,0,0,0.2);
    }

    /* Her ders için özel renk */
    .circle-blue { border-bottom: 6px solid #3498db; color: #3498db; }
    .circle-green { border-bottom: 6px solid #2ecc71; color: #2ecc71; }
    .circle-purple { border-bottom: 6px solid #9b59b6; color: #9b59b6; }
    .circle-red { border-bottom: 6px solid #e74c3c; color: #e74c3c; }
    .circle-orange { border-bottom: 6px solid #f39c12; color: #f39c12; }
    .circle-teal { border-bottom: 6px solid #1abc9c; color: #1abc9c; }
    .circle-indigo { border-bottom: 6px solid #8e44ad; color: #8e44ad; }

    .node-link:hover .circle-blue { background: #3498db; color: white; border-color: #3498db; }
    .node-link:hover .circle-green { background: #2ecc71; color: white; border-color: #2ecc71; }
    .node-link:hover .circle-purple { background: #9b59b6; color: white; border-color: #9b59b6; }
    .node-link:hover .circle-red { background: #e74c3c; color: white; border-color: #e74c3c; }
    .node-link:hover .circle-orange { background: #f39c12; color: white; border-color: #f39c12; }
    .node-link:hover .circle-teal { background: #1abc9c; color: white; border-color: #1abc9c; }
    .node-link:hover .circle-indigo { background: #8e44ad; color: white; border-color: #8e44ad; }

    .node-title {
      font-size: 1rem;
      font-weight: 700;
      color: var(--primary);
      margin-bottom: 0.3rem;
      line-height: 1.2;
    }

    .node-desc {
      font-size: 0.85rem;
      color: #7f8c8d;
      line-height: 1.3;
    }

    /* Akış Hattı (Nehir Metaforu) */
    .flow-lines {
      width: 80%;
      height: 40px;
      background: linear-gradient(to bottom, #ecf0f1 0%, #e67e22 100%);
      clip-path: polygon(20% 0, 80% 0, 100% 100%, 0% 100%);
      opacity: 0.3;
      margin: -10px 0;
    }

    /* Alt Kısım: Ana Hedef (Yapay Öğrenme) */
    .destination-node {
      text-decoration: none;
      color: inherit;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      padding-top: 2rem;
      transition: transform 0.3s ease, opacity 0.3s ease;
    }

    .destination-node:hover {
      transform: scale(1.05);
    }

    .destination-node.hidden {
      display: none;
    }

    .main-circle {
      width: 200px;
      height: 200px;
      border-radius: 50%;
      background: linear-gradient(135deg, var(--accent) 0%, #f1c40f 100%);
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 5rem;
      color: white;
      box-shadow: 0 10px 40px rgba(230,126,34,0.4);
      border: 6px solid white;
      margin-bottom: 1.5rem;
      position: relative;
    }

    .main-circle::after {
      content: '';
      position: absolute;
      top: -10px; left: -10px; right: -10px; bottom: -10px;
      border-radius: 50%;
      border: 2px solid var(--accent);
      animation: pulse 2s infinite;
    }

    @keyframes pulse {
      0% { transform: scale(0.9); opacity: 1; }
      100% { transform: scale(1.3); opacity: 0; }
    }

    .main-label {
      font-size: 1.5rem;
      font-weight: 800;
      color: var(--primary);
      margin-bottom: 0.5rem;
    }

    .main-sublabel {
      font-size: 1rem;
      color: #7f8c8d;
      background: white;
      padding: 0.5rem 1rem;
      border-radius: 20px;
      box-shadow: 0 2px 10px rgba(0,0,0,0.05);
    }

    /* Footer */
    footer {
      text-align: center;
      padding: 3rem 1rem;
      margin-top: 4rem;
      color: #95a5a6;
      font-size: 0.9rem;
      border-top: 1px solid #ecf0f1;
    }

    footer a {
      color: var(--accent);
      text-decoration: none;
    }

    /* Responsive */
    @media (max-width: 768px) {
      .source-nodes {
        grid-template-columns: repeat(2, 1fr);
        gap: 1.5rem;
      }
      .big-circle { width: 100px; height: 100px; font-size: 2.5rem; }
      .main-circle { width: 160px; height: 160px; font-size: 4rem; }
      .main-label { font-size: 1.3rem; }
    }

    @media (max-width: 480px) {
      .source-nodes { grid-template-columns: 1fr; }
    }