/* ==========================================================================
   Happy Choi — personal site, version 2
   Plain CSS. Light and dark themes. No build step, no framework.
   ========================================================================== */

/* --- Theme tokens ------------------------------------------------------- */

:root {
  --bg:         #ffffff;
  --surface:    #f7f7f6;
  --border:     #d8d8d4;
  --text:       #1d1d1b;
  --text-muted: #5c5c57;
  --accent:     #14509b;
  --accent-soft:#e8eef7;
  --shadow:     0 1px 2px rgba(0, 0, 0, .06);
  --font-body:  "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, Helvetica, Arial, sans-serif;
  --font-mono:  Consolas, "SF Mono", Monaco, "Courier New", monospace;
  --page-width: 880px;
}

:root[data-theme="dark"] {
  --bg:         #16181c;
  --surface:    #1e2126;
  --border:     #33373e;
  --text:       #e7e8ea;
  --text-muted: #a2a6ad;
  --accent:     #79aef5;
  --accent-soft:#232c39;
  --shadow:     0 1px 2px rgba(0, 0, 0, .4);
}

/* --- Base -------------------------------------------------------------- */

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

html {
  /* Keeps anchor links clear of the sticky nav bar. */
  scroll-padding-top: 4.5rem;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

/* Only animate the theme flip, and only when the user allows motion. */
@media (prefers-reduced-motion: no-preference) {
  body { transition: background-color .18s ease, color .18s ease; }
}

h1, h2, h3, h4 {
  line-height: 1.25;
  margin: 0 0 .5em;
  font-weight: 650;
}

h1 { font-size: 1.9rem; letter-spacing: -.015em; }
h2 { font-size: 1.35rem; }
h3 { font-size: 1.05rem; }
h4 { font-size: .95rem; }

p { margin: 0 0 1em; }

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

hr {
  border: 0;
  border-top: 1px solid var(--border);
  margin: 2.5rem 0;
}

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 2px;
}

/* Visible only to screen readers, until focused. */
.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 100;
  padding: .6rem 1rem;
  background: var(--accent);
  color: #fff;
}
.skip-link:focus {
  left: .5rem;
  top: .5rem;
}

/* --- Top bar ----------------------------------------------------------- */

.nav {
  position: sticky;
  top: 0;
  z-index: 20;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
}

.nav__inner {
  max-width: var(--page-width);
  margin: 0 auto;
  padding: .5rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.nav__name {
  font-weight: 700;
  font-size: 1rem;
  color: var(--text);
  text-decoration: none;
  letter-spacing: -.01em;
  white-space: nowrap;
}
.nav__name:hover { color: var(--accent); }

.nav__links {
  display: flex;
  gap: .25rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav__links a {
  display: inline-block;
  padding: .4rem .75rem;
  border-radius: 4px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: .95rem;
  border: 1px solid transparent;
}
.nav__links a:hover {
  color: var(--text);
  background: var(--surface);
}

/* Marks the page you are currently on. */
.nav__links a[aria-current="page"] {
  color: var(--text);
  font-weight: 600;
  border-color: var(--border);
  background: var(--surface);
}

.nav__end {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: .5rem;
}

/* --- Theme toggle ------------------------------------------------------ */

.theme-toggle {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  padding: .4rem .7rem;
  font: inherit;
  font-size: .9rem;
  color: var(--text-muted);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 4px;
  cursor: pointer;
}
.theme-toggle:hover {
  color: var(--text);
  background: var(--surface);
}
.theme-toggle svg {
  width: 1rem;
  height: 1rem;
  flex: none;
}

/* Show the sun in dark mode, the moon in light mode — the icon is the
   action you get by clicking, which reads more naturally than the state. */
.theme-toggle .icon-sun  { display: none; }
:root[data-theme="dark"] .theme-toggle .icon-sun  { display: block; }
:root[data-theme="dark"] .theme-toggle .icon-moon { display: none; }

/* --- Page frame -------------------------------------------------------- */

.wrap {
  max-width: var(--page-width);
  margin: 0 auto;
  padding: 2.25rem 1.25rem 1rem;
}

.lede {
  font-size: 1.05rem;
  color: var(--text-muted);
  max-width: 62ch;
}

.page-head {
  padding-bottom: 1.25rem;
  margin-bottom: 1.75rem;
  border-bottom: 1px solid var(--border);
}

/* --- Sections ---------------------------------------------------------- */

.section { margin: 0 0 2.5rem; }

.section > h2 {
  padding-bottom: .4rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 1.1rem;
}

/* --- Home hero --------------------------------------------------------- */

.hero {
  display: flex;
  gap: 2rem;
  align-items: flex-start;
  flex-wrap: wrap;
  margin-bottom: 2.5rem;
}

.hero__text { flex: 1 1 22rem; }
.hero__text h1 { margin-bottom: .6rem; }

.hero__aside {
  flex: 0 0 15rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  padding: 1.1rem;
  box-shadow: var(--shadow);
}

.hero__aside h2 {
  font-size: .95rem;
  border: 0;
  padding: 0;
  margin-bottom: .5rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: .06em;
}

.hero__aside dl {
  margin: 0;
  font-size: .92rem;
}
.hero__aside dt {
  color: var(--text-muted);
  font-size: .8rem;
  text-transform: uppercase;
  letter-spacing: .05em;
  margin-top: .7rem;
}
.hero__aside dd {
  margin: .1rem 0 0;
  overflow-wrap: anywhere;
}
.hero__aside dl > dt:first-child { margin-top: 0; }

/* --- Inline link row --------------------------------------------------- */

.linkrow {
  list-style: none;
  margin: 0 0 1.5rem;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: .5rem;
}

.linkrow a {
  display: inline-block;
  padding: .45rem .85rem;
  font-size: .92rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: var(--surface);
  color: var(--text);
  text-decoration: none;
}
.linkrow a:hover {
  border-color: var(--accent);
  color: var(--accent);
}
.linkrow a.is-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.linkrow a.is-primary:hover { opacity: .9; color: #fff; }
:root[data-theme="dark"] .linkrow a.is-primary { color: #10131a; }

/* --- CV entries -------------------------------------------------------- */

/* An entry is a date column plus a body column. A rule is drawn above every
   entry (including the first) to separate it from the section heading, which
   is itself underlined — matching how a printed CV is laid out. */
.entry {
  display: grid;
  grid-template-columns: 10.5rem 1fr;
  gap: .25rem 1.5rem;
  padding: 1.1rem 0;
  border-top: 1px solid var(--border);
}
.entry:last-child { padding-bottom: 0; }

.entry__when {
  color: var(--text-muted);
  font-size: .89rem;
  padding-top: .15rem;
}

/* The right-hand column of a single-column entry. */
.entry__body > :last-child { margin-bottom: 0; }
.entry__body h3 { margin-bottom: .15rem; }

.entry__org {
  color: var(--text-muted);
  font-size: .93rem;
  margin-bottom: .5rem;
}

.entry__body ul {
  margin: 0;
  padding-left: 1.15rem;
}
.entry__body li { margin-bottom: .35rem; }

/* Compact tag list, used for skills and coursework. */
.tags {
  list-style: none;
  margin: .3rem 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: .35rem;
}
.tags li {
  font-size: .84rem;
  padding: .15rem .5rem;
  border: 1px solid var(--border);
  border-radius: 3px;
  background: var(--surface);
  color: var(--text-muted);
}

/* Two-column block for skills: label on the left, values on the right. */
.facts {
  display: grid;
  grid-template-columns: 10.5rem 1fr;
  gap: .6rem 1.5rem;
  margin: 0;
  font-size: .95rem;
}
.facts dt {
  color: var(--text-muted);
  font-weight: 600;
}
.facts dd { margin: 0; }

/* --- Project write-ups ------------------------------------------------- */

/* Small muted line under a page or entry heading, e.g. a supervisor note. */
.meta {
  color: var(--text-muted);
  font-size: .92rem;
  margin: .1rem 0 .6rem;
}

/* A dated phase nested inside one longer entry, e.g. the terms of a research
   project. Indented under a left rule so the nesting is visible. */
.subentry {
  border-left: 2px solid var(--border);
  padding: 0 0 .1rem 1rem;
  margin: 1rem 0 0;
}
.subentry__head {
  display: flex;
  flex-wrap: wrap;
  gap: .25rem .75rem;
  align-items: baseline;
  margin-bottom: .35rem;
}
.subentry__head h4 {
  margin: 0;
  font-size: .98rem;
}
.subentry__when {
  color: var(--text-muted);
  font-size: .87rem;
}
.subentry > ul { margin: 0; }
.subentry > ul > li { margin-bottom: .3rem; }
.subentry > ul > li:last-child { margin-bottom: 0; }

.project {
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  padding: 1.25rem;
  margin-bottom: 1.5rem;
}
.project h2 { font-size: 1.15rem; margin-bottom: .25rem; }
.project h3 {
  font-size: .95rem;
  margin: 1.2rem 0 .5rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: .05em;
}
.project > :last-child { margin-bottom: 0; }

/* --- Footer ------------------------------------------------------------ */

.foot {
  border-top: 1px solid var(--border);
  margin-top: 3rem;
  padding: 1.5rem 1.25rem 2.5rem;
  font-size: .9rem;
  color: var(--text-muted);
}
.foot__inner {
  max-width: var(--page-width);
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  gap: .5rem 1.5rem;
  align-items: baseline;
}
.foot__links {
  margin-left: auto;
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

/* --- Small screens ----------------------------------------------------- */

@media (max-width: 640px) {
  h1 { font-size: 1.6rem; }

  .nav__inner { padding: .5rem .9rem; }
  .nav__end { margin-left: 0; width: 100%; }
  .theme-toggle { width: 100%; justify-content: center; }

  .wrap { padding: 1.5rem .9rem 1rem; }

  .hero__aside { flex-basis: 100%; }

  /* Stack CV entries so dates sit above the description. */
  .entry,
  .facts {
    grid-template-columns: 1fr;
    gap: .2rem;
  }
  .entry__when { padding-top: 0; }
}

/* --- Printing ---------------------------------------------------------- */

@media print {
  .nav, .foot, .theme-toggle, .skip-link { display: none; }
  .wrap { max-width: none; padding: 0; }
  body { font-size: 11.5pt; }
  .entry { break-inside: avoid; }
  a { color: inherit; text-decoration: none; }
}