:root {
    --primary: #6366f1;
    --primary-hover: #4f46e5;
    --bg: #ffffff;
    --text: #1f2937;
    --text-muted: #6b7280;
    --border: #e5e7eb;
    --card-bg: #f9fafb;
    --font-main: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
}

[data-theme="dark"] {
    --bg: #0f172a;
    --text: #f1f5f9;
    --text-muted: #94a3b8;
    --border: #334155;
    --card-bg: #1e293b;
}

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

body {
    font-family: var(--font-main);
    background-color: var(--bg);
    color: var(--text);
    line-height: 1.6;
    transition: background-color 0.3s, color 0.3s;
}

header {
    padding: 2rem 1rem;
    text-align: center;
    border-bottom: 1px solid var(--border);
    margin-bottom: 2rem;
}

nav {
    display: flex;
    justify-content: center;
    gap: 2rem;
    margin-top: 1rem;
}

nav a {
    text-decoration: none;
    color: var(--primary);
    font-weight: 600;
    transition: color 0.2s;
}

nav a:hover {
    color: var(--primary-hover);
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 1.5rem 4rem;
}

h1 { font-size: 2.5rem; margin-bottom: 0.5rem; }
h2 { font-size: 1.75rem; margin-top: 2rem; margin-bottom: 1rem; color: var(--primary); }
h3 { font-size: 1.25rem; margin-top: 1.5rem; margin-bottom: 0.75rem; }

p { margin-bottom: 1rem; }
ul { margin-bottom: 1rem; padding-left: 1.5rem; }
li { margin-bottom: 0.5rem; }

.card {
    background-color: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 2rem;
    margin-top: 2rem;
}

.footer {
    text-align: center;
    padding: 2rem;
    border-top: 1px solid var(--border);
    color: var(--text-muted);
    font-size: 0.875rem;
}

.theme-toggle {
    position: fixed;
    top: 1rem;
    right: 1rem;
    background: var(--card-bg);
    border: 1px solid var(--border);
    padding: 0.5rem;
    border-radius: 50%;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1);
}

@media (max-width: 640px) {
    h1 { font-size: 2rem; }
    .container { padding: 0 1rem 3rem; }
    nav { flex-direction: column; align-items: center; gap: 0.5rem; }
}