/* Base reset-ish */
*,
*::before,
*::after {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 0;
    font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text",
        "Helvetica Neue", Helvetica, Arial, sans-serif;
    background: linear-gradient(to bottom, #e8f3ff, #f8fbff);
    color: #1a1a1a;
    transition: background 0.3s ease, color 0.3s ease;
}

/* Layout */

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 96px 24px 64px;
}

/* Header */

.site-header {
    position: sticky;
    top: 0;
    z-index: 10;
    backdrop-filter: blur(18px);
    background: rgba(248, 251, 255, 0.7);
    border-bottom: 1px solid rgba(180, 197, 222, 0.4);
}

.header-inner {
    max-width: 980px;
    margin: 0 auto;
    padding: 14px 24px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
}

.logo {
    font-weight: 500;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    font-size: 0.9rem;
}

/* Nav */

.nav {
    display: flex;
    gap: 18px;
    align-items: center;
}

.nav-link {
    text-decoration: none;
    font-size: 0.95rem;
    opacity: 0.7;
    padding-bottom: 2px;
    border-bottom: 1px solid transparent;
    transition: opacity 0.2s ease, border-color 0.2s ease;
    color: inherit;
}

.nav-link:hover {
    opacity: 1;
}

.nav-link.active {
    opacity: 1;
    border-bottom-color: rgba(60, 110, 180, 0.6);
}

/* Theme toggle */

.theme-toggle {
    border: 1px solid rgba(160, 180, 210, 0.7);
    background: rgba(255, 255, 255, 0.6);
    border-radius: 999px;
    padding: 4px 10px;
    font-size: 0.95rem;
    cursor: pointer;
    line-height: 1;
    transition: background 0.2s ease, border-color 0.2s ease, transform 0.1s ease;
}

.theme-toggle:hover {
    background: rgba(255, 255, 255, 0.9);
}

.theme-toggle:active {
    transform: scale(0.96);
}

/* Hero */

.hero {
    text-align: left;
    margin-bottom: 40px;
}

.hero.small {
    margin-bottom: 24px;
}

.hero h1 {
    font-size: 2.2rem;
    font-weight: 500;
    letter-spacing: 0.02em;
    margin-bottom: 0.8rem;
}

.hero-text {
    font-size: 1.05rem;
    line-height: 1.7;
    max-width: 40rem;
    opacity: 0.9;
}

/* Columns */

.columns {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 20px;
}

.column-card {
    background: rgba(255, 255, 255, 0.84);
    border-radius: 18px;
    padding: 18px 18px 20px;
    box-shadow: 0 18px 40px rgba(64, 99, 153, 0.1);
    border: 1px solid rgba(184, 204, 231, 0.6);
    backdrop-filter: blur(10px);
}

.column-card h2 {
    font-size: 1.1rem;
    margin-top: 0;
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.column-card p {
    font-size: 0.98rem;
    line-height: 1.6;
    margin: 0;
    opacity: 0.9;
}

/* Content blocks */

.content-block {
    margin-bottom: 28px;
    max-width: 46rem;
}

.content-block h2 {
    font-size: 1.2rem;
    margin-bottom: 0.4rem;
    font-weight: 500;
}

.content-block p {
    margin: 0.25rem 0 0;
    line-height: 1.7;
    font-size: 1rem;
    opacity: 0.9;
}

.content-block ul {
    margin: 0.5rem 0 0;
    padding-left: 1.1rem;
}

.content-block li {
    margin-bottom: 0.3rem;
    line-height: 1.6;
    font-size: 1rem;
}

/* Footer */

.site-footer {
    max-width: 900px;
    margin: 0 auto;
    padding: 0 24px 32px;
    font-size: 0.9rem;
    opacity: 0.5;
}

/* Dark mode */

body.dark {
    background: radial-gradient(circle at top, #1f2937 0, #020617 55%, #020617 100%);
    color: #e5e7eb;
}

body.dark .site-header {
    background: rgba(2, 6, 23, 0.88);
    border-bottom-color: rgba(51, 65, 85, 0.8);
}

body.dark .theme-toggle {
    background: rgba(15, 23, 42, 0.8);
    border-color: rgba(75, 85, 99, 0.9);
    color: #e5e7eb;
}

body.dark .theme-toggle:hover {
    background: rgba(15, 23, 42, 1);
}

body.dark .nav-link.active {
    border-bottom-color: rgba(129, 140, 248, 0.9);
}

body.dark .column-card {
    background: rgba(15, 23, 42, 0.95);
    border-color: rgba(55, 65, 81, 0.9);
    box-shadow: 0 18px 45px rgba(15, 23, 42, 0.9);
}

body.dark .site-footer {
    opacity: 0.5;
}

/* Responsive */

@media (max-width: 640px) {
    .header-inner {
        padding-inline: 16px;
    }

    .container {
        padding-inline: 16px;
        padding-top: 80px;
    }

    .hero h1 {
        font-size: 1.8rem;
    }
}