/* =========================================================
   UG Advising (Mathematics, SNU) — Light Theme
   Clean, accessible, responsive. Includes optional dark mode
   via prefers-color-scheme for robustness.
   ========================================================= */

:root{
  /* Core palette (light) */
  --bg: #f6f7fb;
  --surface: #ffffff;
  --surface-2: #fbfbfd;
  --text: #0f172a;
  --muted: #475569;
  --muted-2: #64748b;

  --accent: #2563eb;     /* blue */
  --accent-2: #16a34a;   /* green */
  --accent-soft: rgba(37, 99, 235, .10);

  --border: rgba(15, 23, 42, .12);
  --border-2: rgba(15, 23, 42, .08);

  --shadow: 0 10px 30px rgba(15, 23, 42, .08);
  --shadow-sm: 0 6px 18px rgba(15, 23, 42, .06);

  --radius: 16px;
  --radius-sm: 12px;

  --max: 1100px;
  --font: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji","Segoe UI Emoji";
  --mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono","Courier New", monospace;

  --focus-ring: 0 0 0 3px rgba(37, 99, 235, .25);
}

/* Optional dark mode for users who prefer it */
@media (prefers-color-scheme: dark){
  :root{
    --bg: #0b1220;
    --surface: #0f172a;
    --surface-2: #111c33;
    --text: #eaf0ff;
    --muted: #bac4da;
    --muted-2:#9fb0cf;

    --accent: #7bd3ff;
    --accent-2:#a6ffcb;
    --accent-soft: rgba(123, 211, 255, .12);

    --border: rgba(255,255,255,.14);
    --border-2: rgba(255,255,255,.10);

    --shadow: 0 12px 34px rgba(0,0,0,.35);
    --shadow-sm: 0 8px 22px rgba(0,0,0,.30);

    --focus-ring: 0 0 0 3px rgba(123, 211, 255, .30);
  }
}

/* Base */
*{ box-sizing: border-box; }
html,body{ height:100%; }
body{
  margin:0;
  font-family: var(--font);
  color: var(--text);
  line-height: 1.6;
  background:
    radial-gradient(1100px 700px at 15% 10%, rgba(37,99,235,.10), transparent 55%),
    radial-gradient(900px 650px at 90% 30%, rgba(22,163,74,.08), transparent 60%),
    var(--bg);
}

img{ max-width:100%; height:auto; }
a{ color: inherit; text-decoration: none; }
a:hover{ text-decoration: underline; }
p{ margin: .65rem 0; }
ul{ margin: .65rem 0; }
strong{ font-weight: 700; }

.container{
  width: min(100% - 2rem, var(--max));
  margin-inline: auto;
}

.skip-link{
  position:absolute;
  left:-999px;
  top:0;
  padding:.6rem .9rem;
  border-radius: var(--radius-sm);
  background: var(--text);
  color: var(--surface);
  z-index:1000;
}
.skip-link:focus{
  left: .85rem;
  top: .85rem;
  outline:none;
  box-shadow: var(--focus-ring);
}

/* Header / Nav */
header.site-header{
  position: sticky;
  top: 0;
  z-index: 999;
  border-bottom: 1px solid var(--border);
  background: color-mix(in srgb, var(--surface) 86%, transparent);
  backdrop-filter: blur(10px);
}

.navbar{
  display:flex;
  align-items:center;
  justify-content: space-between;
  gap: 1rem;
  padding: .85rem 0;
}

.brand{
  display:flex;
  align-items:center;
  gap:.75rem;
  min-width: 220px;
}
.brand-mark{
  width: 40px;
  height: 40px;
  border-radius: 14px;
  background: linear-gradient(135deg, color-mix(in srgb, var(--accent) 85%, #fff), color-mix(in srgb, var(--accent-2) 70%, #fff));
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--border-2);
}
.brand-title{
  display:flex;
  flex-direction:column;
  line-height: 1.1;
}
.brand-title strong{
  font-size: 1.02rem;
  letter-spacing: .2px;
}
.brand-title span{
  color: var(--muted);
  font-size: .88rem;
}

/* Mobile menu */
#nav-toggle{ display:none; }

.nav-toggle-label{
  display:none;
  cursor:pointer;
  padding:.55rem .7rem;
  border: 1px solid var(--border);
  border-radius: 14px;
  user-select:none;
  background: color-mix(in srgb, var(--surface) 88%, transparent);
}
.nav-toggle-label:hover{ box-shadow: var(--shadow-sm); }

.hamburger{
  width: 22px;
  height: 16px;
  position: relative;
}
.hamburger span{
  position:absolute;
  left:0;
  right:0;
  height: 2px;
  background: var(--text);
  border-radius: 99px;
  opacity: .9;
}
.hamburger span:nth-child(1){ top:0; }
.hamburger span:nth-child(2){ top:7px; opacity:.75; }
.hamburger span:nth-child(3){ bottom:0; opacity:.6; }

.nav{
  display:flex;
  align-items:center;
  justify-content:flex-end;
  flex-wrap: wrap;
  gap:.25rem;
}

.nav .tab{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  padding:.56rem .78rem;
  border-radius: 14px;
  color: var(--muted);
  border: 1px solid transparent;
  transition: background .15s ease, border-color .15s ease, color .15s ease;
}
.nav .tab:hover{
  text-decoration:none;
  color: var(--text);
  background: color-mix(in srgb, var(--surface) 78%, var(--accent-soft));
  border-color: var(--border);
}
.nav .tab.active{
  color: var(--accent);
  background: var(--accent-soft);
  border-color: color-mix(in srgb, var(--accent) 30%, transparent);
}

.nav a[href="course.html"]{ order: 1; }
.nav a[href="elective.html"]{ order: 2; }
.nav a[href="minor-specialization.html"]{ order: 3; }
.nav .nav-dropdown{ order: 4; }
.nav a[href="downloads.html"]{ order: 5; }
.nav a[href="community-qna.html"]{ order: 6; }
.nav a[href="form.html"]{ order: 7; }

.nav-dropdown{
  position: relative;
}
.nav-dropdown summary{
  cursor: pointer;
  list-style: none;
  gap: .42rem;
}
.nav-dropdown summary::-webkit-details-marker{ display:none; }
.nav-dropdown summary.tab::after{
  content: "";
  width: .45rem;
  height: .45rem;
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: translateY(-.12rem) rotate(45deg);
  transition: transform .15s ease;
}
.nav-dropdown[open] summary.tab::after{
  transform: translateY(.12rem) rotate(225deg);
}
.submenu{
  position:absolute;
  right:0;
  top: calc(100% + .35rem);
  min-width: 180px;
  display:none;
  gap:.15rem;
  padding:.45rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--surface) 96%, transparent);
  box-shadow: var(--shadow);
}
.nav-dropdown[open] .submenu,
.nav-dropdown:hover .submenu,
.nav-dropdown:focus-within .submenu{
  display:grid;
}
.submenu a{
  padding:.55rem .7rem;
  border-radius: 10px;
  color: var(--muted);
}
.submenu a:hover,
.submenu a.active{
  text-decoration:none;
  color: var(--accent);
  background: var(--accent-soft);
}

/* Buttons */
.cta{ display:flex; align-items:center; gap:.5rem; }

.button{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  gap:.5rem;
  padding:.62rem .95rem;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: color-mix(in srgb, var(--surface) 90%, transparent);
  color: var(--text);
  text-decoration:none;
  transition: transform .06s ease, box-shadow .15s ease, background .15s ease, border-color .15s ease;
}
.button:hover{
  text-decoration:none;
  box-shadow: var(--shadow-sm);
  border-color: color-mix(in srgb, var(--accent) 25%, var(--border));
}
.button:active{ transform: translateY(1px); }
.button:focus{ outline:none; box-shadow: var(--focus-ring); }

.button.primary{
  background: var(--accent);
  border-color: color-mix(in srgb, var(--accent) 85%, #000);
  color: #fff;
}
.button.primary:hover{
  background: color-mix(in srgb, var(--accent) 88%, #000);
  border-color: color-mix(in srgb, var(--accent) 92%, #000);
}

/* Main layout */
main{ padding: 2rem 0 3rem; }

.hero{
  display:grid;
  grid-template-columns: 1.25fr .75fr;
  gap: 1.25rem;
  align-items: stretch;
  margin-top: 1rem;
}

.card{
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.card .pad{ padding: 1.2rem; }

h1,h2,h3{
  line-height: 1.25;
  margin: 0 0 .55rem;
}
h1{ font-size: clamp(1.7rem, 3.1vw, 2.35rem); }
h2{ font-size: clamp(1.2rem, 2.2vw, 1.55rem); }
h3{ font-size: 1.05rem; }

.lead{
  color: var(--muted);
  font-size: 1.02rem;
  max-width: 72ch;
}

.badge{
  display:inline-flex;
  align-items:center;
  gap:.35rem;
  padding:.26rem .6rem;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--muted);
  font-size: .86rem;
  background: color-mix(in srgb, var(--surface) 84%, transparent);
}

/* Grid helpers */
.grid{
  display:grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 1rem;
  margin-top: 1rem;
}
.col-4{ grid-column: span 4; }
.col-6{ grid-column: span 6; }
.col-8{ grid-column: span 8; }
.col-12{ grid-column: span 12; }

.tile{
  height:100%;
  background: color-mix(in srgb, var(--surface-2) 92%, transparent);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  box-shadow: var(--shadow-sm);
  transition: transform .08s ease, box-shadow .15s ease, border-color .15s ease;
}
.tile:hover{
  text-decoration:none;
  transform: translateY(-1px);
  border-color: color-mix(in srgb, var(--accent) 22%, var(--border));
  box-shadow: var(--shadow);
}
.tile p{
  margin: .45rem 0 0;
  color: var(--muted);
}
.tile .top{
  display:flex;
  align-items:flex-start;
  justify-content: space-between;
  gap: .8rem;
}
.kicker{
  color: var(--muted-2);
  font-size: .92rem;
  margin: 0;
}

/* Lists / section blocks */
.list{
  margin: .4rem 0 0;
  padding-left: 1.1rem;
  color: var(--muted);
}
.list li{ margin: .35rem 0; }

.section{ margin-top: 1.25rem; }
.section .section-head{
  display:flex;
  align-items:flex-end;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: .6rem;
}

.hr{
  border: 0;
  border-top: 1px solid var(--border);
  margin: 1.15rem 0;
}

.notice{
  border-left: 4px solid color-mix(in srgb, var(--accent) 70%, transparent);
  padding: .7rem .9rem;
  background: color-mix(in srgb, var(--accent-soft) 85%, var(--surface));
  border-radius: var(--radius-sm);
  color: var(--muted);
}

/* Details / FAQ */
details{
  border: 1px solid var(--border);
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  border-radius: var(--radius-sm);
  padding: .7rem .9rem;
}
details + details{ margin-top: .6rem; }
summary{
  cursor: pointer;
  font-weight: 700;
}
summary:focus{
  outline:none;
  box-shadow: var(--focus-ring);
  border-radius: 10px;
}
details p{ margin: .55rem 0 0; color: var(--muted); }

/* Forms */
form{ display:grid; gap: .9rem; }
label{ font-weight: 700; }

input, select, textarea{
  width: 100%;
  background: color-mix(in srgb, var(--surface) 96%, transparent);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: .68rem .78rem;
  color: var(--text);
  font: inherit;
}
textarea{ min-height: 150px; resize: vertical; }

input:focus, select:focus, textarea:focus{
  outline:none;
  box-shadow: var(--focus-ring);
  border-color: color-mix(in srgb, var(--accent) 45%, var(--border));
}

.form-row{
  display:grid;
  grid-template-columns: 1fr 1fr;
  gap: .9rem;
}

/* Inline code */
.code{
  font-family: var(--mono);
  font-size: .92rem;
  color: color-mix(in srgb, var(--text) 92%, transparent);
  background: color-mix(in srgb, var(--surface) 88%, transparent);
  border: 1px solid var(--border);
  padding: .15rem .42rem;
  border-radius: 8px;
  white-space: nowrap;
}

/* Footer */
footer{
  border-top: 1px solid var(--border);
  padding: 1.5rem 0;
  color: var(--muted);
  font-size: .94rem;
  background: color-mix(in srgb, var(--surface) 88%, transparent);
}
.footer-row{
  display:flex;
  flex-wrap: wrap;
  align-items:center;
  justify-content: space-between;
  gap: .8rem;
}
.small{ font-size: .9rem; color: var(--muted); }

/* Responsive */
@media (max-width: 940px){
  .nav-toggle-label{ display:inline-flex; align-items:center; gap:.6rem; }
  .nav{
    position:absolute;
    left:0; right:0;
    top: 68px;
    margin-inline: auto;
    width: min(100% - 2rem, var(--max));
    background: color-mix(in srgb, var(--surface) 92%, transparent);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: .65rem;
    display:none;
    flex-direction: column;
    align-items: stretch;
  }
  #nav-toggle:checked ~ .nav{ display:flex; }
  .nav .tab{ width: 100%; }
  .nav-dropdown{ width: 100%; }
  .submenu{
    position: static;
    min-width: 100%;
    box-shadow: none;
    margin-top: .25rem;
  }
}

@media (max-width: 760px){
  .hero{ grid-template-columns: 1fr; }
  .form-row{ grid-template-columns: 1fr; }
}

/* Print */
@media print{
  header.site-header, .cta, .nav-toggle-label{ display:none !important; }
  body{ background: #fff !important; color:#000 !important; }
  .card, .tile, details{ box-shadow:none !important; }
}