:root {
        --bg-color: #0f172a;
        --card-bg: #1e293b;
        --text-color: #f8fafc;
        --border-color: #334155;

        --reactive-nonmetal: #0284c7;
        --noble-gas: #7c3aed;
        --alkali-metal: #dc2626;
        --alkaline-earth: #ea580c;
        --metalloid: #0d9488;
        --post-transition: #16a34a;
        --transition-metal: #d97706;
        --lanthanide: #c026d3;
        --actinide: #db2777;
        --unknown: #475569;
      }

      * {
        box-sizing: border-box;
        margin: 0;
        padding: 0;
        font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
      }

      body {
        background-color: var(--bg-color);
        color: var(--text-color);
        padding: 20px;
        display: flex;
        flex-direction: column;
        align-items: center;
        min-height: 100vh;
      }

      header {
        text-align: center;
        margin-bottom: 20px;
      }

      header h1 {
        font-size: 2.2rem;
        color: #38bdf8;
        margin-bottom: 5px;
      }

      header p {
        color: #94a3b8;
        font-size: 0.95rem;
      }

      .controls {
        display: flex;
        flex-wrap: wrap;
        gap: 8px;
        justify-content: center;
        max-width: 1000px;
        margin-bottom: 25px;
      }

      .filter-btn {
        background-color: var(--card-bg);
        border: 1px solid var(--border-color);
        color: var(--text-color);
        padding: 6px 12px;
        border-radius: 20px;
        font-size: 0.8rem;
        cursor: pointer;
        transition: all 0.2s ease;
      }

      .filter-btn:hover,
      .filter-btn.active {
        background-color: #38bdf8;
        color: #0f172a;
        font-weight: bold;
        border-color: #38bdf8;
      }

      .periodic-table {
        display: grid;
        grid-template-columns: repeat(18, minmax(50px, 1fr));
        gap: 5px;
        max-width: 1250px;
        width: 100%;
        overflow-x: auto;
        padding-bottom: 10px;
      }

      .element {
        background-color: var(--card-bg);
        border: 1px solid var(--border-color);
        border-radius: 6px;
        padding: 3px;
        aspect-ratio: 1;
        display: flex;
        flex-direction: column;
        justify-content: space-between;
        cursor: pointer;
        transition:
          transform 0.2s,
          box-shadow 0.2s,
          opacity 0.2s;
      }

      .element:hover {
        transform: scale(1.18);
        z-index: 10;
        box-shadow: 0 0 12px rgba(56, 189, 248, 0.6);
        border-color: #38bdf8;
      }

      .element.dimmed {
        opacity: 0.2;
      }

      .number {
        font-size: 0.6rem;
        color: #94a3b8;
      }

      .symbol {
        font-size: 1rem;
        font-weight: bold;
        text-align: center;
      }

      .name {
        font-size: 0.5rem;
        text-align: center;
        white-space: nowrap;
        overflow: hidden;
        text-overflow: ellipsis;
        color: #cbd5e1;
      }

      .reactive-nonmetal {
        border-top: 3px solid var(--reactive-nonmetal);
      }
      .noble-gas {
        border-top: 3px solid var(--noble-gas);
      }
      .alkali-metal {
        border-top: 3px solid var(--alkali-metal);
      }
      .alkaline-earth {
        border-top: 3px solid var(--alkaline-earth);
      }
      .metalloid {
        border-top: 3px solid var(--metalloid);
      }
      .post-transition {
        border-top: 3px solid var(--post-transition);
      }
      .transition-metal {
        border-top: 3px solid var(--transition-metal);
      }
      .lanthanide {
        border-top: 3px solid var(--lanthanide);
      }
      .actinide {
        border-top: 3px solid var(--actinide);
      }
      .unknown {
        border-top: 3px solid var(--unknown);
      }

      .gap {
        grid-column: span 1;
      }

      .lanthanide-marker,
      .actinide-marker {
        display: flex;
        align-items: center;
        justify-content: center;
        font-size: 0.65rem;
        color: #94a3b8;
        border: 1px dashed var(--border-color);
        border-radius: 6px;
      }

      .series-spacer {
        grid-column: 1 / -1;
        height: 15px;
      }

      footer {
        margin-top: 30px;
        color: #64748b;
        font-size: 0.85rem;
      }

      .modal-overlay {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: rgba(15, 23, 42, 0.8);
        backdrop-filter: blur(4px);
        display: flex;
        justify-content: center;
        align-items: center;
        opacity: 0;
        pointer-events: none;
        transition: opacity 0.3s ease;
        z-index: 100;
      }

      .modal-overlay.active {
        opacity: 1;
        pointer-events: auto;
      }

      .modal-card {
        background-color: var(--card-bg);
        border: 1px solid var(--border-color);
        border-radius: 12px;
        padding: 24px;
        max-width: 350px;
        width: 90%;
        box-shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
        position: relative;
      }

      .close-btn {
        position: absolute;
        top: 12px;
        right: 15px;
        background: none;
        border: none;
        color: #94a3b8;
        font-size: 1.2rem;
        cursor: pointer;
      }

      .modal-header {
        display: flex;
        align-items: center;
        gap: 15px;
        margin-bottom: 15px;
      }

      .modal-symbol {
        font-size: 2.2rem;
        font-weight: bold;
        background: #0f172a;
        padding: 10px 15px;
        border-radius: 8px;
        border: 1px solid var(--border-color);
        color: #38bdf8;
      }

      .modal-info h2 {
        font-size: 1.3rem;
      }
      .modal-info p {
        font-size: 0.85rem;
        color: #94a3b8;
      }

      .modal-details {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 10px;
        font-size: 0.85rem;
        margin-top: 15px;
        border-top: 1px solid var(--border-color);
        padding-top: 15px;
      }

      .detail-item span {
        display: block;
        color: #94a3b8;
        font-size: 0.75rem;
      }