:root {
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary: #64748b;
    --bg: #f8fafc;
    --card: #ffffff;
    --text: #1e293b;
    --text-secondary: #475569;
    --border: #e2e8f0;
    --shadow: rgba(0,0,0,0.05);
}

html.dark {
    --primary: #3b82f6;
    --primary-hover: #60a5fa;
    --secondary: #94a3b8;
    --bg: #0f172a;
    --card: #1e293b;
    --text: #e2e8f0;
    --text-secondary: #94a3b8;
    --border: #334155;
    --shadow: rgba(0,0,0,0.2);
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background-color: var(--bg);
    color: var(--text);
    margin: 0;
    padding: 0;
    transition: background-color 0.3s, color 0.3s;
    line-height: 1.5;
}

header {
    background: var(--card);
    padding: 1rem 1.5rem;
    box-shadow: 0 2px 4px var(--shadow);
    border-bottom: 3px solid var(--primary);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 1200px;
    margin: 0 auto;
}

header h1 {
    margin: 0;
    color: var(--primary);
    font-size: 1.5rem;
}

header h1 a {
    text-decoration: none;
    color: inherit;
}

.theme-switcher {
    cursor: pointer;
    background: none;
    border: none;
    font-size: 1.25rem;
    color: var(--text);
    padding: 8px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background-color 0.2s;
}

.theme-switcher:hover {
    background-color: var(--bg);
}

.nav-container {
    max-width: 1200px;
    margin: 1rem auto 0;
    padding: 0 20px;
}

.nav-breadcrumb {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.nav-breadcrumb a {
    color: var(--primary);
    text-decoration: none;
}

.nav-breadcrumb a:hover {
    text-decoration: underline;
}

.container {
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 20px;
}

footer {
    text-align: center;
    padding: 3rem 1rem;
    color: var(--secondary);
    font-size: 0.9rem;
    border-top: 1px solid var(--border);
    background: var(--card);
    margin-top: 4rem;
}

footer a {
    color: var(--primary);
    text-decoration: none;
    margin: 0 10px;
}

footer a:hover {
    text-decoration: underline;
}

/* Common UI Elements */
.btn {
    display: inline-block;
    padding: 0.8rem 1.5rem;
    border-radius: 8px;
    font-weight: 600;
    text-align: center;
    cursor: pointer;
    transition: all 0.2s;
    border: none;
}

.btn-primary {
    background-color: var(--primary);
    color: white;
}

.btn-primary:hover {
    background-color: var(--primary-hover);
}

.btn-secondary {
    background-color: var(--secondary);
    color: white;
}

.card {
    background: var(--card);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px -1px var(--shadow);
    border: 1px solid var(--border);
}

.hidden {
    display: none !important;
}