:root {
    --bg-light: #ffffff;
    --bg-dark: #1e293b;
    --text-primary: #334155;
    --text-secondary: #64748b;
    --accent-orange: #f97316;
    --border-color: #e2e8f0;
    --font-sans: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    --sidebar-width: 260px;
}

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

body {
    font-family: var(--font-sans);
    color: var(--text-primary);
    background-color: var(--bg-light);
    line-height: 1.6;
}

.page-layout {
    display: flex;
    min-height: 100vh;
}

/* Sidebar */
.sidebar-nav {
    width: var(--sidebar-width);
    background-color: var(--bg-dark);
    color: white;
    position: fixed;
    height: 100vh;
    display: flex;
    flex-direction: column;
    padding: 2rem;
    z-index: 100;
}

.brand-logo {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 3rem;
}

.logo-icon {
    width: 40px;
    height: 40px;
    background-color: var(--accent-orange);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    font-size: 1.2rem;
    border-radius: 4px;
}

.logo-text {
    font-weight: 700;
    letter-spacing: 1px;
    font-size: 1.1rem;
}

.nav-menu {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.nav-item {
    text-decoration: none;
    color: #94a3b8;
    display: flex;
    align-items: center;
    gap: 15px;
    padding: 10px;
    border-radius: 6px;
    transition: all 0.3s;
}

.nav-item:hover, .nav-item.active {
    background-color: rgba(255,255,255,0.1);
    color: white;
}

.nav-num {
    font-family: monospace;
    color: var(--accent-orange);
    font-size: 0.9rem;
}

.sidebar-footer {
    font-size: 0.8rem;
    color: #64748b;
    border-top: 1px solid #334155;
    padding-top: 1rem;
}

/* Main Content */
.content-scroll {
    margin-left: var(--sidebar-width);
    flex: 1;
    padding: 0;
}

.knowledge-block {
    padding: 4rem 5rem;
    min-height: 80vh;
    border-bottom: 1px solid var(--border-color);
}

.alt-bg {
    background-color: #f8fafc;
}

.block-header {
    margin-bottom: 3rem;
}

.block-header h2 {
    font-size: 2.5rem;
    color: var(--bg-dark);
    margin-bottom: 1rem;
}

.header-line {
    width: 60px;
    height: 4px;
    background-color: var(--accent-orange);
}

/* Intro Section */
.lead-text {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: 3rem;
    max-width: 800px;
}

.info-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
}

.info-card {
    background: white;
    padding: 2rem;
    border-radius: 8px;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    border-top: 4px solid var(--accent-orange);
}

.info-card h4 {
    margin-bottom: 1rem;
    font-size: 1.2rem;
}

.info-card p {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

/* Structures Section */
.structure-list {
    display: flex;
    flex-direction: column;
    gap: 3rem;
}

.structure-item {
    display: flex;
    gap: 2rem;
    background: white;
    padding: 1.5rem;
    border-radius: 12px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.struct-img {
    width: 300px;
    height: 200px;
    flex-shrink: 0;
    overflow: hidden;
    border-radius: 8px;
}

.struct-img img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.5s;
}

.structure-item:hover .struct-img img {
    transform: scale(1.05);
}

.struct-info h3 {
    margin-bottom: 0.5rem;
    color: var(--bg-dark);
}

.struct-info p {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

/* Materials Table */
.material-table-wrapper {
    overflow-x: auto;
}

.data-table {
    width: 100%;
    border-collapse: collapse;
    background: white;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    border-radius: 8px;
    overflow: hidden;
}

.data-table th, .data-table td {
    padding: 1.2rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.data-table th {
    background-color: var(--bg-dark);
    color: white;
    font-weight: 600;
    text-transform: uppercase;
    font-size: 0.85rem;
    letter-spacing: 1px;
}

.data-table tr:last-child td {
    border-bottom: none;
}

.data-table tr:hover {
    background-color: #f1f5f9;
}

/* Timeline */
.timeline {
    position: relative;
    max-width: 800px;
    margin: 0 auto;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 50px;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--border-color);
}

.timeline-item {
    position: relative;
    margin-bottom: 3rem;
    padding-left: 80px;
}

.time-point {
    position: absolute;
    left: 0;
    top: 0;
    width: 100px;
    text-align: right;
    font-weight: bold;
    color: var(--accent-orange);
    font-size: 1.1rem;
}

.time-content {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    position: relative;
}

.time-content::before {
    content: '';
    position: absolute;
    left: -10px;
    top: 20px;
    width: 20px;
    height: 20px;
    background: white;
    border: 4px solid var(--accent-orange);
    border-radius: 50%;
    z-index: 1;
}

.time-content h4 {
    margin-bottom: 0.5rem;
    color: var(--bg-dark);
}

.time-content p {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

/* Footer */
.main-footer {
    padding: 2rem 5rem;
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.9rem;
    background: var(--bg-dark);
    color: #94a3b8;
}

@media (max-width: 768px) {
    .page-layout {
        flex-direction: column;
    }
    .sidebar-nav {
        width: 100%;
        height: auto;
        position: relative;
        padding: 1rem;
    }
    .nav-menu {
        flex-direction: row;
        overflow-x: auto;
        padding-bottom: 1rem;
    }
    .nav-item {
        white-space: nowrap;
    }
    .content-scroll {
        margin-left: 0;
    }
    .knowledge-block {
        padding: 2rem;
    }
    .structure-item {
        flex-direction: column;
    }
    .struct-img {
        width: 100%;
        height: 200px;
    }
    .timeline::before {
        left: 20px;
    }
    .timeline-item {
        padding-left: 50px;
    }
    .time-point {
        width: auto;
        left: 0;
        top: -25px;
        text-align: left;
        font-size: 0.9rem;
    }
    .time-content::before {
        left: -34px;
    }
}