:root {
    --blue-950: #0f2540;
    --blue-900: #1a3a5c;
    --blue-700: #2d5a8e;
    --blue-600: #3d6ea8;
    --blue-100: #ddeaf7;
    --blue-50: #f0f6fc;
    --white: #fff;
    --gray-800: #1e2d3d;
    --gray-600: #4a6072;
    --gray-400: #7a93a8;
    --gray-200: #cfdbe8;
    --gray-100: #f4f7fa;
    --font-sans: system-ui, -apple-system, sans-serif;
    --font-mono: ui-monospace, monospace;
}

*,
*::before,
*::after {
    box-sizing: border-box;
}

body {
    margin: 0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    background: var(--white);
    color: var(--gray-800);
    font-family: var(--font-sans);
    font-size: 1rem;
    line-height: 1.6;
}

/* ── Header ── */

header {
    background: var(--blue-900);
    padding: 0.875rem 0;
}

header .container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 2rem;
    display: flex;
    align-items: center;
}

header a {
    color: var(--white);
    text-decoration: none;
    font-weight: 600;
    font-size: 1.1rem;
    letter-spacing: -0.01em;
}

header a:hover {
    color: var(--blue-100);
}

/* ── Main ── */

main {
    flex: 1;
    padding: 2.5rem 0;
}

/* ── Two-column page layout ── */

.page {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 2rem;
    display: grid;
    grid-template-columns: 1fr 260px;
    gap: 3rem;
    align-items: start;
}

@media (width <= 760px) {
    .page {
        grid-template-columns: 1fr;
        gap: 2rem;
    }
}

/* ── Article nav sidebar ── */

.article-nav {
    background: var(--blue-50);
    border: 1px solid var(--gray-200);
    border-radius: 8px;
    padding: 1.25rem 1.5rem;
    position: sticky;
    top: 1.5rem;
}

.article-nav h2 {
    margin: 0 0 0.875rem;
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--gray-400);
}

.article-nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
}

.article-nav li {
    border-top: 1px solid var(--gray-200);
    padding: 0.6rem 0;
}

.article-nav li:first-child {
    border-top: none;
}

.article-nav li.current a {
    color: var(--blue-950);
    font-weight: 600;
}

.article-nav a {
    display: block;
    color: var(--blue-700);
    text-decoration: none;
    font-size: 0.875rem;
    line-height: 1.4;
}

.article-nav a:hover {
    color: var(--blue-950);
    text-decoration: underline;
}

.article-nav time {
    display: block;
    font-size: 0.75rem;
    color: var(--gray-400);
    margin-top: 0.15rem;
}

/* ── Footer ── */

footer {
    background: var(--gray-100);
    border-top: 1px solid var(--gray-200);
    padding: 1rem 0;
    color: var(--gray-400);
    font-size: 0.8rem;
    text-align: center;
}

/* ── Typography ── */

h1,
h2,
h3 {
    line-height: 1.2;
    color: var(--gray-800);
}

h1 {
    margin: 0 0 0.5rem;
    font-size: 2rem;
    letter-spacing: -0.02em;
}

h2 {
    font-size: 1.35rem;
    margin: 2rem 0 0.5rem;
}

a {
    color: var(--blue-700);
}

a:hover {
    color: var(--blue-950);
}

code {
    font-family: var(--font-mono);
    font-size: 0.875em;
    background: var(--blue-50);
    border: 1px solid var(--gray-200);
    padding: 0.1em 0.35em;
    border-radius: 4px;
}

pre {
    background: var(--gray-100);
    border: 1px solid var(--gray-200);
    border-radius: 6px;
    padding: 1.25rem 1.5rem;
    overflow-x: auto;
    font-size: 0.875rem;
}

pre code {
    background: none;
    border: none;
    padding: 0;
}

/* ── Home page ── */

.home-intro {
    padding-top: 0.25rem;
}

.home-intro h1 {
    font-size: 2.25rem;
    margin-bottom: 0.5rem;
}

.home-intro p {
    color: var(--gray-600);
    font-size: 1.05rem;
    margin: 0;
}

/* ── Article page ── */

article {
    min-width: 0; /* prevent grid blowout */
}

article > header {
    background: none;
    padding: 0 0 1.25rem;
    margin-bottom: 2rem;
    border-bottom: 1px solid var(--gray-200);
}

article > header h1 {
    margin-bottom: 0.4rem;
}

.meta {
    color: var(--gray-400);
    font-size: 0.875rem;
    margin: 0;
}

article p,
article li {
    color: var(--gray-800);
    max-width: 68ch;
}