/* ---------------------------------------------------------------
   Control Systems I - TA site
   Placeholder styling. Swap the tokens below to restyle the site.
   --------------------------------------------------------------- */

:root {
  --accent:        #1f4e79;
  --accent-soft:   #e8f0f8;
  --bg:            #ffffff;
  --bg-alt:        #f6f7f9;
  --text:          #1c1f23;
  --text-muted:    #5a626b;
  --border:        #e2e5ea;
  --placeholder:   #a4560c;
  --placeholder-bg:#fdf3e6;

  --radius: 10px;
  --wrap: 960px;
  --font-body: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-head: Georgia, "Times New Roman", serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --accent:        #7fb2e5;
    --accent-soft:   #16283a;
    --bg:            #14171a;
    --bg-alt:        #1b1f23;
    --text:          #e6e8ea;
    --text-muted:    #9aa3ad;
    --border:        #2b3138;
    --placeholder:   #e0a765;
    --placeholder-bg:#2a2115;
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

.wrap {
  width: 100%;
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 0 20px;
}

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

h1, h2, h3 { font-family: var(--font-head); line-height: 1.25; }

code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 1px 5px;
}

.skip-link { position: absolute; left: -9999px; }
.skip-link:focus {
  left: 12px; top: 12px;
  z-index: 100;
  background: var(--bg);
  border: 2px solid var(--accent);
  padding: 8px 14px;
  border-radius: var(--radius);
}

/* --- header ---------------------------------------------------- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 62px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text);
  font-weight: 600;
}

.brand-mark {
  display: inline-grid;
  place-items: center;
  width: 34px; height: 34px;
  border-radius: 8px;
  background: var(--accent);
  color: #fff;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.5px;
}

@media (prefers-color-scheme: dark) {
  .brand-mark { color: #0f1519; }
}

.nav { display: flex; gap: 22px; }

.nav a {
  text-decoration: none;
  color: var(--text-muted);
  font-size: 15px;
  padding: 6px 0;
  border-bottom: 2px solid transparent;
}
.nav a:hover { color: var(--text); border-bottom-color: var(--accent); }

.nav-toggle {
  display: none;
  font: inherit;
  font-size: 14px;
  background: var(--bg-alt);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 7px 12px;
  cursor: pointer;
}

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

.hero {
  background: var(--bg-alt);
  border-bottom: 1px solid var(--border);
  padding: 64px 0 56px;
  margin-bottom: 48px;
}

.eyebrow {
  margin: 0 0 8px;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
  color: var(--accent);
}

.hero h1 { margin: 0 0 14px; font-size: clamp(2rem, 5vw, 2.9rem); }

.lede { margin: 0 0 10px; font-size: 1.12rem; max-width: 62ch; }

.byline { margin: 0 0 26px; color: var(--text-muted); font-size: 0.95rem; }

.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; }

.btn {
  display: inline-block;
  text-decoration: none;
  font-size: 15px;
  font-weight: 500;
  padding: 10px 20px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
}
.btn:hover { border-color: var(--accent); }

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.btn-primary:hover { opacity: 0.9; }

@media (prefers-color-scheme: dark) {
  .btn-primary { color: #0f1519; }
}

/* --- sections -------------------------------------------------- */

section { margin-bottom: 52px; scroll-margin-top: 80px; }

section > h2 {
  font-size: 1.5rem;
  margin: 0 0 6px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}

.section-note { margin: 0 0 22px; color: var(--text-muted); font-size: 0.95rem; }

.card {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
}

.card h3 { margin: 4px 0 8px; font-size: 1.12rem; }
.card p:last-child, .card ul:last-child { margin-bottom: 0; }
.card ul { margin: 0; padding-left: 20px; }
.card li { margin-bottom: 6px; }

.callout { border-left: 3px solid var(--accent); background: var(--accent-soft); }
.callout h2 { margin: 0 0 12px; font-size: 1.2rem; border: 0; padding: 0; }

.announce-list { list-style: none; margin: 0; padding: 0; }
.announce-list li { padding: 8px 0; border-top: 1px solid var(--border); }
.announce-list li:first-child { border-top: 0; }
.announce-list time {
  display: inline-block;
  min-width: 130px;
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--text-muted);
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 16px;
}
.grid-2 { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }

.tag {
  margin: 0;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: var(--accent);
}

.links { display: flex; flex-wrap: wrap; gap: 14px; font-size: 14px; margin-bottom: 0; }

/* --- table ----------------------------------------------------- */

.table-scroll { overflow-x: auto; border: 1px solid var(--border); border-radius: var(--radius); }

table { width: 100%; border-collapse: collapse; font-size: 15px; }

th, td { text-align: left; padding: 11px 16px; border-bottom: 1px solid var(--border); }

th {
  background: var(--bg-alt);
  font-weight: 600;
  font-size: 13px;
  letter-spacing: 0.4px;
  text-transform: uppercase;
  color: var(--text-muted);
}

tbody tr:last-child td { border-bottom: 0; }

/* --- placeholder marker ---------------------------------------- */
/* Every .ph span is content still to be filled in. The highlight
   disappears on its own as you replace the text; delete this rule
   when you no longer want the reminder.                            */

.ph {
  background: var(--placeholder-bg);
  color: var(--placeholder);
  border-radius: 3px;
  padding: 0 4px;
  font-style: italic;
}

/* --- footer ---------------------------------------------------- */

.site-footer {
  border-top: 1px solid var(--border);
  background: var(--bg-alt);
  padding: 30px 0;
  margin-top: 20px;
  color: var(--text-muted);
  font-size: 14px;
}
.site-footer p { margin: 0 0 4px; }

.fine { font-size: 13px; color: var(--text-muted); }

/* --- responsive ------------------------------------------------ */

@media (max-width: 640px) {
  body { font-size: 16px; }
  .nav-toggle { display: block; }
  .nav {
    display: none;
    position: absolute;
    top: 62px; left: 0; right: 0;
    flex-direction: column;
    gap: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    padding: 8px 20px 14px;
  }
  .nav.open { display: flex; }
  .nav a { padding: 10px 0; border-bottom: 1px solid var(--border); }
  .hero { padding: 44px 0 40px; }
  .announce-list time { display: block; min-width: 0; }
}