/* ============================================
   CSS Custom Properties (Variables)
   ============================================ */
:root {
    /* Colors - Accessible and pleasant */
    --color-bg: #fafaf9;
    --color-text: #1a1a1a;
    --color-text-muted: #525252;
    --color-link: #2563eb;
    --color-link-hover: #1d4ed8;
    --color-border: #e5e5e5;
    --color-accent: #7c3aed;
    --color-surface: #ffffff;

    /* Typography */
    --font-base: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
    --font-size-base: 18px;
    --line-height-base: 1.7;
    --line-height-tight: 1.3;

    /* Spacing */
    --space-xs: 0.5rem;
    --space-sm: 1rem;
    --space-md: 1.5rem;
    --space-lg: 2rem;
    --space-xl: 3rem;

    /* Layout */
    --max-width: 1200px;
    --content-width: 65ch;
    --sidebar-width: 280px;
    --gap: 2rem;
}

/* ============================================
   Reset and Base Styles
   ============================================ */
*, *::before, *::after {
    box-sizing: border-box;
}

html {
    font-size: var(--font-size-base);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    margin: 0;
    font-family: var(--font-base);
    line-height: var(--line-height-base);
    color: var(--color-text);
    background-color: var(--color-bg);
}

/* ============================================
   Skip Link (Accessibility)
   ============================================ */
.skip-link {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--color-accent);
    color: white;
    padding: var(--space-sm);
    text-decoration: none;
    z-index: 100;
}

.skip-link:focus {
    top: 0;
}

/* ============================================
   Typography
   ============================================ */
h1, h2, h3, h4, h5, h6 {
    margin: var(--space-lg) 0 var(--space-md);
    line-height: var(--line-height-tight);
    font-weight: 700;
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.25rem; }
h5 { font-size: 1.125rem; }
h6 { font-size: 1rem; }

p {
    margin: 0 0 var(--space-md);
}

a {
    color: var(--color-link);
    text-decoration: none;
    border-bottom: 1px solid transparent;
    transition: border-color 0.2s;
}

a:hover {
    color: var(--color-link-hover);
    border-bottom-color: var(--color-link-hover);
}

a:focus {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}

code {
    font-family: var(--font-mono);
    font-size: 0.9em;
    background: var(--color-surface);
    padding: 0.2em 0.4em;
    border-radius: 3px;
    border: 1px solid var(--color-border);
}

pre {
    overflow-x: auto;
    padding: var(--space-md);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 4px;
}

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

blockquote {
    margin: var(--space-md) 0;
    padding-left: var(--space-md);
    border-left: 4px solid var(--color-accent);
    color: var(--color-text-muted);
    font-style: italic;
}

/* ============================================
   Header
   ============================================ */
.site-header {
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    padding: var(--space-md) 0;
}

.header-content {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 var(--space-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--space-md);
}

.site-branding a {
    border: none;
}

.site-title {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-text);
}

.site-tagline {
    margin: var(--space-xs) 0 0;
    color: var(--color-text-muted);
    font-size: 0.9rem;
}

.main-nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    gap: var(--space-md);
}

.main-nav a {
    font-weight: 500;
}

.main-nav a[aria-current="page"] {
    color: var(--color-accent);
}

/* ============================================
   Main Layout Container (CSS Grid)
   ============================================ */
.container {
    max-width: var(--max-width);
    margin: var(--space-xl) auto;
    padding: 0 var(--space-md);
    display: grid;
    grid-template-columns: 1fr var(--sidebar-width);
    gap: var(--gap);
    align-items: start;
}

/* ============================================
   Main Content
   ============================================ */
main {
    min-width: 0; /* Prevent grid blowout */
}

.article-header {
    margin-bottom: var(--space-lg);
}

.article-header h1 {
    margin: 0 0 var(--space-sm);
}

.article-header time {
    display: block;
    color: var(--color-text-muted);
    font-size: 0.9rem;
}

.article-content {
    max-width: var(--content-width);
}

.article-content img {
    max-width: 100%;
    height: auto;
    border-radius: 4px;
}

.article-footer {
    margin-top: var(--space-xl);
    padding-top: var(--space-md);
    border-top: 1px solid var(--color-border);
}

.tags {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-xs);
}

.tags li a {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 20px;
    font-size: 0.85rem;
    transition: background-color 0.2s;
}

.tags li a:hover {
    background: var(--color-accent);
    color: white;
    border-color: var(--color-accent);
}

/* ============================================
   List Pages
   ============================================ */
.list-header {
    margin-bottom: var(--space-xl);
}

.list-header h1 {
    margin-top: 0;
}

.list-item {
    margin-bottom: var(--space-xl);
    padding-bottom: var(--space-lg);
    border-bottom: 1px solid var(--color-border);
}

.list-item:last-child {
    border-bottom: none;
}

.list-item h2 {
    margin: 0 0 var(--space-xs);
    font-size: 1.5rem;
}

.list-item h2 a {
    color: var(--color-text);
}

.list-item h2 a:hover {
    color: var(--color-link);
}

.list-item time {
    display: block;
    color: var(--color-text-muted);
    font-size: 0.9rem;
    margin-bottom: var(--space-sm);
}

.list-item .summary {
    color: var(--color-text-muted);
}

/* ============================================
   Sidebar
   ============================================ */
aside {
    position: sticky;
    top: var(--space-md);
}

.sidebar-section {
    background: var(--color-surface);
    padding: var(--space-md);
    border-radius: 4px;
    border: 1px solid var(--color-border);
    margin-bottom: var(--space-md);
}

.sidebar-section h2 {
    margin: 0 0 var(--space-md);
    font-size: 1.125rem;
    color: var(--color-text);
}

.sidebar-section ul {
    list-style: none;
    margin: 0;
    padding: 0;
}

.sidebar-section li {
    margin-bottom: var(--space-xs);
}

.sidebar-section a {
    display: block;
    padding: 0.25rem 0;
}

/* ============================================
   Footer
   ============================================ */
.site-footer {
    margin-top: var(--space-xl);
    padding: var(--space-lg) 0;
    background: var(--color-surface);
    border-top: 1px solid var(--color-border);
    text-align: center;
    color: var(--color-text-muted);
}

.footer-content {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 var(--space-md);
}

.footer-content p {
    margin: var(--space-xs) 0;
    font-size: 0.9rem;
}

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 768px) {
    :root {
        --font-size-base: 16px;
    }

    .container {
        grid-template-columns: 1fr;
        margin: var(--space-md) auto;
    }

    aside {
        position: static;
    }

    .header-content {
        flex-direction: column;
        align-items: flex-start;
    }

    .main-nav ul {
        flex-direction: column;
        gap: var(--space-sm);
    }

    h1 { font-size: 2rem; }
    h2 { font-size: 1.5rem; }
}

@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* ============================================
   Print Styles
   ============================================ */
@media print {
    .site-header,
    .site-footer,
    aside,
    .skip-link {
        display: none;
    }

    .container {
        grid-template-columns: 1fr;
    }

    a {
        text-decoration: underline;
    }
}