/* =========================================================
       CSS RESET & GLOBAL STYLES (AI Modern Glassmorphism Theme)
       ========================================================= */
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
      font-family: 'Prompt', sans-serif;
    }

    body {
      min-height: 100vh;
      background: #090a0f;
      background-image: 
        radial-gradient(circle at 15% 15%, rgba(112, 0, 255, 0.25) 0%, transparent 40%),
        radial-gradient(circle at 85% 85%, rgba(0, 242, 254, 0.2) 0%, transparent 40%),
        radial-gradient(circle at 50% 50%, rgba(13, 14, 25, 0.9) 0%, #050508 100%);
      color: #ffffff;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      overflow-x: hidden;
      position: relative;
      padding: 100px 1rem 2rem 1rem; /* เพิ่ม padding-top เพื่อเว้นพื้นที่ให้ Navbar */
    }

    /* Ambient Floating Glow Bubbles in Background */
    #particle-container {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      pointer-events: none;
      z-index: 1;
      overflow: hidden;
    }

    .particle {
      position: absolute;
      border-radius: 50%;
      filter: blur(8px);
      opacity: 0.5;
      animation: floatUp linear infinite;
    }

    @keyframes floatUp {
      0% {
        transform: translateY(100vh) scale(0.8);
        opacity: 0;
      }
      20% {
        opacity: 0.6;
      }
      80% {
        opacity: 0.6;
      }
      100% {
        transform: translateY(-20vh) scale(1.2);
        opacity: 0;
      }
    }

    /* =========================================================
       NAVBAR / HEADER STYLES (ส่วนที่เพิ่มใหม่)
       ========================================================= */
    .navbar {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 70px;
      background: rgba(1, 15, 78, 0.75);
      backdrop-filter: blur(15px);
      -webkit-backdrop-filter: blur(15px);
      border-bottom: 1px solid rgba(255, 255, 255, 0.08);
      display: flex;
      justify-content: space-between;
      align-items: center;
      padding: 0 5%;
      z-index: 100;
      box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
    }

    .nav-brand {
      display: flex;
      align-items: center;
      gap: 12px;
      text-decoration: none;
    }

    .nav-logo {
      width: 42px;
      height: 42px;
      object-fit: contain;
      border-radius: 50%;
      box-shadow: 0 0 10px rgba(255, 255, 255, 0.2);
    }

    .nav-title {
      font-size: 1.25rem;
      font-weight: 600;
      color: #ffffff;
      letter-spacing: 0.5px;
    }

    .nav-menu {
      display: flex;
      list-style: none;
      gap: 2rem;
    }

    .nav-menu li a {
      color: #cbd5e1;
      text-decoration: none;
      font-size: 1rem;
      font-weight: 400;
      transition: all 0.3s ease;
      position: relative;
    }

    .nav-menu li a:hover {
      color: #00f2fe;
      text-shadow: 0 0 8px rgba(0, 242, 254, 0.6);
    }

    .nav-menu li a::after {
      content: '';
      position: absolute;
      width: 0%;
      height: 2px;
      bottom: -4px;
      left: 0;
      background: linear-gradient(90deg, #00f2fe, #7000ff);
      transition: width 0.3s ease;
      border-radius: 2px;
    }

    .nav-menu li a:hover::after {
      width: 100%;
    }

    /* =========================================================
       MAIN CONTAINER & CARD STYLES
       ========================================================= */
    .main-container {
      position: relative;
      z-index: 10;
      width: 100%;
      max-width: 850px;
      background: rgba(255, 255, 255, 0.03);
      backdrop-filter: blur(16px);
      -webkit-backdrop-filter: blur(16px);
      border: 1px solid rgba(255, 255, 255, 0.08);
      border-radius: 28px;
      padding: 3rem 2rem;
      box-shadow: 0 30px 60px rgba(0, 0, 0, 0.6),
                  inset 0 1px 0 rgba(255, 255, 255, 0.1);
      text-align: center;
      margin-top: 20px;
    }

    /* Page Header inside Card */
    .page-header h2 {
      font-size: 2.2rem;
      font-weight: 700;
      background: linear-gradient(135deg, #ffffff 0%, #a5b4fc 50%, #00f2fe 100%);
      background-clip: text;
      -webkit-background-clip: text;
      -webkit-text-fill-color: transparent;
      margin-bottom: 2.5rem;
      letter-spacing: 0.5px;
      text-shadow: 0 10px 20px rgba(0, 242, 254, 0.15);
    }

    /* Grid Layout for Grade Levels */
    .grid-container {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
      gap: 1.5rem;
    }

    /* AI Style Glass Cards */
    .card-item {
      background: rgba(255, 255, 255, 0.025);
      border: 1px solid rgba(255, 255, 255, 0.06);
      border-radius: 20px;
      padding: 1.8rem 1.5rem;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
      position: relative;
      overflow: hidden;
    }

    .card-item::before {
      content: '';
      position: absolute;
      top: 0;
      left: -100%;
      width: 100%;
      height: 100%;
      background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.05), transparent);
      transition: 0.5s;
    }

    .card-item:hover::before {
      left: 100%;
    }

    .card-item:hover {
      transform: translateY(-8px);
      background: rgba(255, 255, 255, 0.05);
      border-color: rgba(255, 255, 255, 0.2);
    }

    .card-item h3 {
      font-size: 1.25rem;
      font-weight: 500;
      color: #f1f5f9;
      margin-bottom: 1.2rem;
    }

    /* =========================================================
       NEON BUTTONS
       ========================================================= */
    .neon-btn {
      width: 100%;
      padding: 0.75rem 1.5rem;
      font-size: 1rem;
      font-weight: 600;
      border: none;
      border-radius: 12px;
      cursor: pointer;
      color: #ffffff;
      text-decoration: none;
      display: inline-block;
      transition: all 0.3s ease;
      position: relative;
      z-index: 1;
      outline: none;
    }

    .btn-p13 {
      background: linear-gradient(135deg, #00c6ff, #0072ff);
      box-shadow: 0 4px 15px rgba(0, 198, 255, 0.3);
    }
    .btn-p13:hover {
      box-shadow: 0 0 25px rgba(0, 198, 255, 0.8);
      transform: scale(1.03);
    }

    .btn-p46 {
      background: linear-gradient(135deg, #f72585, #7209b7);
      box-shadow: 0 4px 15px rgba(247, 37, 133, 0.3);
    }
    .btn-p46:hover {
      box-shadow: 0 0 25px rgba(247, 37, 133, 0.8);
      transform: scale(1.03);
    }

    .btn-m13 {
      background: linear-gradient(135deg, #00f2fe, #4facfe);
      box-shadow: 0 4px 15px rgba(0, 242, 254, 0.3);
    }
    .btn-m13:hover {
      box-shadow: 0 0 25px rgba(0, 242, 254, 0.8);
      transform: scale(1.03);
    }

    .btn-m46 {
      background: linear-gradient(135deg, #ff0844, #ffb199);
      box-shadow: 0 4px 15px rgba(255, 8, 68, 0.3);
    }
    .btn-m46:hover {
      box-shadow: 0 0 25px rgba(255, 8, 68, 0.8);
      transform: scale(1.03);
    }

    /* Responsive Design */
    @media (max-width: 768px) {
      .navbar {
        padding: 0 1.5rem;
      }
      .nav-menu {
        gap: 1rem;
      }
      .nav-menu li a {
        font-size: 0.9rem;
      }
      .nav-title {
        font-size: 1.05rem;
      }
    }

    @media (max-width: 600px) {
      body {
        padding-top: 130px; /* เพิ่มพื้นที่ด้านบนสำหรับเมนู 2 บรรทัดบนมือถือ */
      }
      .navbar {
        flex-direction: column;
        height: auto;
        padding: 0.8rem 1rem;
        gap: 0.5rem;
      }
      .main-container {
        padding: 2rem 1.25rem;
      }
      .page-header h2 {
        font-size: 1.5rem;
      }
      .grid-container {
        grid-template-columns: 1fr;
      }
    }