* {
    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: 30px;
}

h1 {
    color: #2c3e50;
    font-weight: normal;
    font-size: 28px;
    margin-bottom: 10px;
}

body.dark h1 {
    color: #ecf0f1;
}

.subtitle {
    color: #666;
    font-size: 16px;
    margin-bottom: 15px;
}

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: 20px;
}

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

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

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

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

.stats-bar {
    display: flex;
    justify-content: center;
    gap: 40px;
    margin-bottom: 30px;
    flex-wrap: wrap;
}

.stat {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 32px;
    color: #3498db;
    font-weight: bold;
}

.stat-label {
    font-size: 12px;
    color: #666;
}

body.dark .stat-label {
    color: #aaa;
}


.timeline-container {
    max-width: 900px;
    margin: 0 auto;
    position: relative;
    padding: 20px 0;
}

.timeline-line {
    position: absolute;
    left: 50%;
    top: 0;
    bottom: 0;
    width: 4px;
    background: linear-gradient(to bottom, #3498db, #9b59b6, #e74c3c);
    transform: translateX(-50%);
    border-radius: 2px;
}

.timeline-item {
    position: relative;
    margin-bottom: 30px;
    width: 45%;
    padding: 20px;
    background: white;
    border-radius: 10px;
    box-shadow: 0 3px 15px rgba(0,0,0,0.1);
    transition: transform 0.2s, box-shadow 0.2s;
}

body.dark .timeline-item {
    background: #2d2d44;
}

.timeline-item:hover {
    transform: scale(1.02);
    box-shadow: 0 5px 25px rgba(0,0,0,0.15);
}

.timeline-item.left {
    margin-left: 0;
    margin-right: auto;
}

.timeline-item.right {
    margin-left: auto;
    margin-right: 0;
}

.timeline-item::before {
    content: '';
    position: absolute;
    top: 25px;
    width: 16px;
    height: 16px;
    background: #3498db;
    border-radius: 50%;
    border: 3px solid white;
    box-shadow: 0 0 0 3px #3498db;
}

body.dark .timeline-item::before {
    border-color: #1a1a2e;
}

.timeline-item.left::before {
    right: -8%;
}

.timeline-item.right::before {
    left: -8%;
}

.timeline-item::after {
    content: '';
    position: absolute;
    top: 28px;
    width: 30px;
    height: 3px;
    background: #3498db;
}

.timeline-item.left::after {
    right: -7%;
}

.timeline-item.right::after {
    left: -7%;
}

.timeline-year {
    display: inline-block;
    background: #3498db;
    color: white;
    padding: 5px 12px;
    border-radius: 15px;
    font-size: 14px;
    margin-bottom: 10px;
}

.timeline-year.ancient {
    background: #8e44ad;
}

.timeline-year.era-1700s {
    background: #27ae60;
}

.timeline-year.era-1800s {
    background: #e67e22;
}

.timeline-year.era-1900s {
    background: #e74c3c;
}

.timeline-year.era-2000s {
    background: #1abc9c;
}

.element-symbol {
    display: inline-block;
    width: 50px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    font-size: 22px;
    font-weight: bold;
    border-radius: 8px;
    margin-right: 15px;
    float: left;
}

.element-name {
    font-size: 20px;
    color: #2c3e50;
    margin-bottom: 5px;
}

body.dark .element-name {
    color: #ecf0f1;
}

.element-number {
    font-size: 12px;
    color: #888;
    margin-bottom: 10px;
}

.discoverer {
    font-size: 14px;
    color: #555;
    margin-bottom: 5px;
}

body.dark .discoverer {
    color: #bbb;
}

.discovery-story {
    font-size: 13px;
    color: #666;
    line-height: 1.5;
    clear: both;
    padding-top: 10px;
}

body.dark .discovery-story {
    color: #aaa;
}

.alkali { background: #ffb3ba; color: #333; }
.alkaline { background: #ffdfba; color: #333; }
.transition { background: #ffffba; color: #333; }
.post-transition { background: #baffc9; color: #333; }
.metalloid { background: #bae1ff; color: #333; }
.nonmetal { background: #e2baff; color: #333; }
.halogen { background: #ffbaf3; color: #333; }
.noble { background: #d4baff; color: #333; }
.lanthanide { background: #ffd9ba; color: #333; }
.actinide { background: #c9ffba; color: #333; }
.unknown { background: #ddd; color: #333; }

.no-results {
    text-align: center;
    padding: 40px;
    color: #888;
    font-size: 18px;
}

@media (max-width: 768px) {
    .timeline-line {
        left: 20px;
    }
    
    .timeline-item {
        width: calc(100% - 50px);
        margin-left: 50px !important;
        margin-right: 0 !important;
    }
    
    .timeline-item::before {
        left: -38px !important;
        right: auto !important;
    }
    
    .timeline-item::after {
        left: -30px !important;
        right: auto !important;
        width: 20px;
    }
    
    .stats-bar {
        gap: 20px;
    }
    
    .stat-number {
        font-size: 24px;
    }
    
    .controls {
        flex-direction: column;
        align-items: stretch;
        padding: 0 10px;
    }
    
    .controls input, .controls select, .controls button {
        width: 100%;
    }
    
    h1 {
        font-size: 22px;
    }
}