/* Engineering Knowledge Base - dark theme */

:root {
  --bg: #0d0f12;
  --surface: #161a20;
  --surface-raised: #1c2129;
  --border: #2a3038;
  --text: #e8eaed;
  --text-muted: #9aa3af;
  --accent: #5eead4;
  --accent-hover: #99f6e4;
  --question: #f5c451;
  --code-bg: #1e2430;
  --link: #5eead4;
  --max-width: 52rem;
  --radius: 10px;
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  font-size: 1rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

/* ── Header ── */

header {
  padding: 2.5rem 1.25rem 1.75rem;
  text-align: center;
  border-bottom: 1px solid var(--border);
  background: linear-gradient(180deg, #12151a 0%, var(--bg) 100%);
}

.site-brand {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.85rem;
  margin-bottom: 0.5rem;
}

.site-logo {
  display: block;
  width: 72px;
  height: 72px;
}

header h1 {
  margin: 0 0 0.5rem;
  font-size: clamp(1.5rem, 4vw, 2rem);
  font-weight: 700;
  color: var(--accent);
  letter-spacing: -0.02em;
}

.site-brand h1 {
  margin: 0;
}

.maintainer {
  margin: 1rem auto 0;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.maintainer a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 600;
}

.maintainer a:hover {
  color: var(--accent-hover);
  text-decoration: underline;
}

header > p {
  margin: 0 auto;
  max-width: var(--max-width);
  color: var(--text-muted);
  font-size: 1.05rem;
}

/* Breadcrumb nav inside header */
header nav p {
  margin: 0 0 1.25rem;
  font-size: 0.875rem;
  color: var(--text-muted);
}

header nav a {
  color: var(--text-muted);
  text-decoration: none;
}

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

/* ── Table of contents (Q&A page) ── */

nav[aria-label="Table of contents"] {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 1.5rem 1.25rem;
  border-bottom: 1px solid var(--border);
}

nav[aria-label="Table of contents"] h2 {
  margin: 0 0 0.75rem;
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
}

nav[aria-label="Table of contents"] ol {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

nav[aria-label="Table of contents"] li {
  margin: 0;
}

nav[aria-label="Table of contents"] a {
  display: inline-block;
  padding: 0.35rem 0.75rem;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--text-muted);
  font-size: 0.8rem;
  text-decoration: none;
  transition: color 0.15s, border-color 0.15s, background 0.15s;
}

nav[aria-label="Table of contents"] a:hover {
  color: var(--accent);
  border-color: var(--accent);
  background: rgba(94, 234, 212, 0.06);
}

/* ── Main content ── */

main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 2rem 1.25rem 4rem;
}

section {
  margin-bottom: 2.5rem;
}

section:last-child {
  margin-bottom: 0;
}

h2 {
  margin: 0 0 0.75rem;
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--accent);
  letter-spacing: -0.01em;
}

main > section h3 {
  margin: 1.5rem 0 0.6rem;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text);
}

main > section h3:first-of-type {
  margin-top: 0.75rem;
}

section > p:first-of-type {
  margin-top: 0;
}

p {
  margin: 0 0 1rem;
}

/* Subject / segment list cards (lists that contain links) */
main > section > ul:has(a) {
  margin: 0;
  padding: 0;
  list-style: none;
}

main > section > ul:has(a) > li {
  margin-bottom: 0.75rem;
  padding: 1rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  transition: border-color 0.15s;
}

main > section > ul:has(a) > li:hover {
  border-color: #3d4654;
}

main > section > ul:has(a) > li a {
  color: var(--accent);
  text-decoration: none;
  font-size: 1.05rem;
}

main > section > ul:has(a) > li a:hover {
  color: var(--accent-hover);
  text-decoration: underline;
}

main > section > ul:has(a) > li {
  color: var(--text-muted);
  font-size: 0.95rem;
  line-height: 1.55;
}

/* Regular lists inside sections */
section ul:not(main > section > ul),
section ol {
  margin: 0 0 1rem;
  padding-left: 1.4rem;
}

section li {
  margin-bottom: 0.4rem;
}

section li::marker {
  color: var(--text-muted);
}

/* ── Links ── */

a {
  color: var(--link);
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
}

a:hover {
  color: var(--accent-hover);
}

/* ── Inline code & tags ── */

code {
  padding: 0.15em 0.45em;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--accent);
  font-family: "SF Mono", "Cascadia Code", Consolas, "Liberation Mono", monospace;
  font-size: 0.88em;
}

strong {
  color: #d4dae0;
  font-weight: 600;
}

/* ── Q&A sections (interview page) ── */

main > section[id] {
  padding-top: 0.5rem;
}

main > section[id] > h2 {
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 0.5rem;
}

main > section[id] > p {
  color: var(--text-muted);
  font-size: 0.92rem;
  margin-bottom: 1.25rem;
}

/* Expandable Q&A */
details {
  margin-bottom: 0.65rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: border-color 0.15s;
}

details[open] {
  border-color: #3d5a54;
  background: var(--surface-raised);
}

summary {
  cursor: pointer;
  padding: 0.9rem 1rem 0.9rem 0.75rem;
  font-weight: 600;
  color: var(--question);
  list-style: none;
  display: flex;
  gap: 0.65rem;
  align-items: flex-start;
  line-height: 1.45;
  user-select: none;
}

summary::-webkit-details-marker {
  display: none;
}

summary::before {
  content: "Q";
  flex-shrink: 0;
  margin-top: 0.1em;
  padding: 0.1em 0.45em;
  background: var(--question);
  color: #1a1408;
  font-size: 0.7rem;
  font-weight: 800;
  border-radius: 4px;
  line-height: 1.3;
}

details > div {
  padding: 0 1rem 1rem 2.6rem;
  color: var(--text);
  font-size: 0.95rem;
  line-height: 1.65;
}

details > div p:last-child,
details > div ul:last-child {
  margin-bottom: 0;
}

details > div ul {
  padding-left: 1.25rem;
}

details > div li {
  margin-bottom: 0.5rem;
}

details > div strong {
  color: var(--accent);
}

/* ── Footer ── */

footer {
  padding: 1.5rem 1.25rem;
  text-align: center;
  border-top: 1px solid var(--border);
  background: #0a0c0f;
}

footer p {
  margin: 0;
}

footer small {
  color: var(--text-muted);
  font-size: 0.8rem;
}

footer a {
  color: var(--text-muted);
  text-decoration: none;
}

footer a:hover {
  color: var(--accent);
}

/* ── Responsive ── */

@media (max-width: 600px) {
  header {
    padding: 1.75rem 1rem 1.25rem;
  }

  main {
    padding: 1.5rem 1rem 3rem;
  }

  details > div {
    padding-left: 1rem;
  }

  nav[aria-label="Table of contents"] ol {
    gap: 0.4rem;
  }
}

/* Knowledge article pages */
.learn-page main.article h3 {
  margin: 1.5rem 0 0.5rem;
  font-size: 1.05rem;
  color: #d4dae0;
}

.learn-page main.article h4 {
  margin: 1rem 0 0.4rem;
  font-size: 0.95rem;
  color: var(--text-muted);
}

.learn-page .callout {
  margin: 1.25rem 0;
  padding: 1rem 1.15rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: var(--radius);
}

.learn-page .callout strong {
  color: var(--accent);
}

.learn-page pre {
  margin: 1rem 0;
  padding: 1rem;
  overflow-x: auto;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: 0.88rem;
  line-height: 1.5;
}

.learn-page pre code {
  padding: 0;
  background: none;
  border: none;
  color: var(--text);
  font-size: inherit;
}

.learn-page .refer-link {
  margin: 0.75rem 0 1.25rem;
  color: var(--text-muted);
  line-height: 1.5;
}

.learn-page .refer-link a {
  color: var(--accent);
}

.learn-page table {
  width: 100%;
  margin: 1rem 0 1.25rem;
  border-collapse: collapse;
  font-size: 0.92rem;
}

.learn-page th,
.learn-page td {
  padding: 0.6rem 0.75rem;
  border: 1px solid var(--border);
  text-align: left;
  vertical-align: top;
}

.learn-page th {
  background: var(--surface);
  color: var(--accent);
  font-weight: 600;
}

.learn-page .page-footer-nav {
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.learn-page .page-footer-nav p {
  margin-bottom: 0.5rem;
}

.learn-page .interview-link {
  display: inline-block;
  margin-top: 0.5rem;
  padding: 0.6rem 1rem;
  background: rgba(94, 234, 212, 0.08);
  border: 1px solid #3d5a54;
  border-radius: var(--radius);
  text-decoration: none;
  font-weight: 600;
}

.learn-page .interview-link:hover {
  background: rgba(94, 234, 212, 0.14);
}

/* Hub: two-track layout */
.hub-tracks {
  display: grid;
  gap: 1.5rem;
  margin-bottom: 2rem;
}

@media (min-width: 700px) {
  .hub-tracks {
    grid-template-columns: 1fr 1fr;
  }
}

.hub-track {
  padding: 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}

.hub-track h2 {
  margin-top: 0;
}

.hub-track-learn {
  border-color: #3d5a54;
}

.hub-track-interview {
  border-color: #5a4d3d;
}

.hub-track-interview h2 {
  color: var(--question);
}

/* Interview hub badge on Q&A pages */
header .badge-interview {
  display: inline-block;
  margin-bottom: 0.75rem;
  padding: 0.25rem 0.65rem;
  background: rgba(245, 196, 81, 0.15);
  border: 1px solid #5a4d2a;
  border-radius: 999px;
  color: var(--question);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    transition: none !important;
  }
}