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

body {
    font-family: Georgia, 'Times New Roman', serif;
    background: #f4f1eb;
    min-height: 100vh;
    padding: 20px;
    transition: background 0.3s, color 0.3s;
}

body.dark {
    background: #1a1a2e;
    color: #eee;
}

header {
    text-align: center;
    margin-bottom: 25px;
}

h1 {
    color: #2c3e50;
    font-weight: normal;
    font-size: 28px;
    margin-bottom: 8px;
}

body.dark h1 { color: #ecf0f1; }

.subtitle {
    color: #666;
    font-size: 15px;
    margin-bottom: 12px;
}

body.dark .subtitle { color: #aaa; }

.back-link {
    display: inline-block;
    color: #3498db;
    text-decoration: none;
    padding: 8px 20px;
    border: 1px solid #3498db;
    border-radius: 20px;
    transition: all 0.2s;
}

.back-link:hover {
    background: #3498db;
    color: white;
}

.controls {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 10px;
    margin-bottom: 25px;
}

.controls select, .controls input, .controls button {
    padding: 10px 15px;
    border: 1px solid #ccc;
    border-radius: 5px;
    font-size: 14px;
    font-family: inherit;
}

body.dark .controls select, body.dark .controls input {
    background: #2d2d44;
    color: #eee;
    border-color: #444;
}

.controls button {
    background: #3498db;
    color: white;
    border: none;
    cursor: pointer;
}

.controls button:hover { background: #2980b9; }

.chart-container, .content-section, .facts-section {
    max-width: 900px;
    margin: 0 auto 25px;
    background: white;
    padding: 25px;
    border-radius: 12px;
    box-shadow: 0 3px 15px rgba(0,0,0,0.1);
}

body.dark .chart-container, body.dark .content-section, body.dark .facts-section {
    background: #2d2d44;
}

h3 {
    color: #2c3e50;
    font-weight: normal;
    margin-bottom: 20px;
    text-align: center;
}

body.dark h3 { color: #ecf0f1; }

.bar-item {
    display: flex;
    align-items: center;
    margin-bottom: 12px;
}

.bar-label {
    width: 50px;
    font-weight: bold;
    color: #2c3e50;
}

body.dark .bar-label { color: #ecf0f1; }

.bar-track {
    flex: 1;
    height: 25px;
    background: #ecf0f1;
    border-radius: 12px;
    overflow: hidden;
    margin: 0 10px;
}

body.dark .bar-track { background: #1a1a2e; }

.bar-fill {
    height: 100%;
    border-radius: 12px;
    transition: width 0.5s ease;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    padding-right: 8px;
    color: white;
    font-size: 11px;
    min-width: 30px;
}

.bar-value {
    width: 80px;
    text-align: right;
    font-size: 13px;
    color: #666;
}

body.dark .bar-value { color: #aaa; }


.facts-section ul, .content-section ul {
    margin-left: 20px;
    line-height: 1.8;
    color: #555;
}

body.dark .facts-section ul, body.dark .content-section ul { color: #bbb; }

.grid-2 {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
}

.card {
    background: #f8f9fa;
    padding: 20px;
    border-radius: 10px;
}

body.dark .card { background: #1a1a2e; }

.card h4 {
    color: #2c3e50;
    margin-bottom: 10px;
    font-weight: normal;
}

body.dark .card h4 { color: #ecf0f1; }

.card p {
    color: #666;
    font-size: 14px;
    line-height: 1.6;
}

body.dark .card p { color: #aaa; }

.isotope-card {
    background: #f8f9fa;
    padding: 15px;
    border-radius: 10px;
    margin-bottom: 15px;
}

body.dark .isotope-card { background: #1a1a2e; }

.isotope-card .mass-number {
    font-size: 24px;
    font-weight: bold;
    color: #3498db;
}

.isotope-card .abundance {
    color: #27ae60;
    font-size: 14px;
}

.isotope-card .half-life {
    color: #e74c3c;
    font-size: 13px;
}

.isotope-card .stable {
    color: #27ae60;
}

.safety-category {
    margin-bottom: 25px;
    padding: 20px;
    border-radius: 10px;
}

.safety-category.danger {
    background: #fdecea;
    border-left: 4px solid #e74c3c;
}

body.dark .safety-category.danger { background: #3d2020; }

.safety-category.warning {
    background: #fef9e7;
    border-left: 4px solid #f39c12;
}

body.dark .safety-category.warning { background: #3d3520; }

.safety-category.info {
    background: #eaf2f8;
    border-left: 4px solid #3498db;
}

body.dark .safety-category.info { background: #203040; }

.safety-category h4 {
    margin-bottom: 10px;
    color: #2c3e50;
}

body.dark .safety-category h4 { color: #ecf0f1; }

.solubility-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 13px;
    overflow-x: auto;
    display: block;
}

.solubility-table th, .solubility-table td {
    padding: 10px;
    text-align: center;
    border: 1px solid #ddd;
}

body.dark .solubility-table th, body.dark .solubility-table td {
    border-color: #444;
}

.solubility-table th {
    background: #3498db;
    color: white;
}

.solubility-table td.soluble {
    background: #d5f5e3;
    color: #27ae60;
}

body.dark .solubility-table td.soluble { background: #1e3a2f; }

.solubility-table td.insoluble {
    background: #fadbd8;
    color: #e74c3c;
}

body.dark .solubility-table td.insoluble { background: #3d2020; }

.solubility-table td.slightly {
    background: #fef9e7;
    color: #f39c12;
}

body.dark .solubility-table td.slightly { background: #3d3520; }

.legend-box {
    display: flex;
    justify-content: center;
    gap: 20px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 13px;
}

.legend-color {
    width: 20px;
    height: 20px;
    border-radius: 4px;
}

.legend-color.soluble { background: #27ae60; }
.legend-color.insoluble { background: #e74c3c; }
.legend-color.slightly { background: #f39c12; }

@media (max-width: 600px) {
    .controls { flex-direction: column; align-items: stretch; }
    .controls select, .controls button { width: 100%; }
    .bar-label { width: 35px; font-size: 12px; }
    .bar-value { width: 60px; font-size: 11px; }
    h1 { font-size: 22px; }
    .grid-2 { grid-template-columns: 1fr; }
}