/* ============================================================
   Ekinops Dark Fiber Learning Path
   Dark-blue / slate / cyan optical theme
   ============================================================ */

:root {
  --bg:            #0a1220;
  --bg-2:          #0f1a2e;
  --panel:         #13233d;
  --panel-2:       #182b47;
  --border:        #24405f;
  --border-soft:   #1c3350;
  --text:          #e7eef7;
  --text-dim:      #a9bbd0;
  --text-mute:     #7e93ac;
  --cyan:          #34d3e0;
  --cyan-deep:     #1893a6;
  --blue:          #4b9bff;
  --amber:         #f4b445;
  --green:         #4bd694;
  --red:           #ff6b6b;
  --violet:        #9d8bff;
  --shadow:        0 6px 22px rgba(0,0,0,.35);
  --radius:        10px;
  --maxw:          1080px;
  --mono:          "SFMono-Regular", "JetBrains Mono", Menlo, Consolas, "Liberation Mono", monospace;
  --sans:          system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background:
    radial-gradient(1200px 600px at 80% -10%, rgba(52,211,224,.08), transparent 60%),
    radial-gradient(900px 500px at -10% 10%, rgba(75,155,255,.07), transparent 55%),
    var(--bg);
  color: var(--text);
  font-family: var(--sans);
  line-height: 1.6;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Top bar ---------- */
:root { --topbar-h: 54px; --sidebar-w: 256px; }

.topnav {
  position: sticky;
  top: 0;
  z-index: 60;
  display: flex;
  align-items: center;
  gap: .65rem;
  padding: .7rem 1.1rem;
  background: rgba(10,18,32,.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.brand {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: .2px;
  color: var(--text);
  text-decoration: none;
  white-space: nowrap;
}
.brand span { color: var(--cyan); }

.nav-toggle {
  display: none;
  background: var(--panel);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 1.2rem;
  line-height: 1;
  padding: .3rem .55rem;
  cursor: pointer;
}

/* ---------- Shell: sidebar + content column ---------- */
.shell { display: flex; align-items: flex-start; gap: 0; }

.sidebar {
  flex: 0 0 var(--sidebar-w);
  position: sticky;
  top: var(--topbar-h);
  height: calc(100vh - var(--topbar-h));
  overflow-y: auto;
  padding: 1rem .8rem 2rem;
  background: rgba(15,26,46,.45);
  border-right: 1px solid var(--border);
}

.col { flex: 1 1 auto; min-width: 0; }

.nav-links { display: flex; flex-direction: column; gap: .05rem; }
.nav-group { margin-bottom: 1.05rem; }
.nav-group-title {
  font-size: .68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .11em;
  color: var(--text-mute);
  margin: .1rem .55rem .35rem;
}
.nav-links a {
  color: var(--text-dim);
  text-decoration: none;
  font-size: .875rem;
  padding: .4rem .6rem;
  border-radius: 7px;
  border-left: 2px solid transparent;
  transition: background .15s, color .15s;
}
.nav-links a:hover { color: var(--text); background: var(--panel); }
.nav-links a.active {
  color: var(--text);
  background: rgba(52,211,224,.12);
  border-left-color: var(--cyan);
  font-weight: 600;
}

/* ---------- Layout ---------- */
.content {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 2rem 1.25rem 1rem;
}

h1, h2, h3, h4 { line-height: 1.25; color: var(--text); }
h1 { font-size: 2rem; margin: .2rem 0 1rem; }
h2 {
  font-size: 1.45rem;
  margin: 2.2rem 0 .9rem;
  padding-bottom: .4rem;
  border-bottom: 1px solid var(--border-soft);
}
h3 { font-size: 1.15rem; margin: 1.4rem 0 .6rem; color: var(--cyan); }
h4 { font-size: 1rem; margin: 1rem 0 .4rem; color: var(--text-dim); }

p { color: var(--text-dim); }
a { color: var(--blue); }
strong { color: var(--text); }

ul, ol { color: var(--text-dim); }
li { margin: .25rem 0; }

.lead { font-size: 1.1rem; color: var(--text); }
.muted { color: var(--text-mute); font-size: .9rem; }

/* ---------- Hero ---------- */
.hero {
  background:
    linear-gradient(135deg, rgba(52,211,224,.12), rgba(75,155,255,.06)),
    var(--panel);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 2rem 1.75rem;
  box-shadow: var(--shadow);
  margin-bottom: 1.5rem;
}
.hero h1 { margin-top: 0; }
.hero p { color: var(--text); font-size: 1.08rem; max-width: 70ch; }

/* ---------- Cards ---------- */
.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.1rem 1.25rem;
  margin: 1rem 0;
  box-shadow: var(--shadow);
}
.card h3 { margin-top: .2rem; }

/* ---------- Grids ---------- */
.grid { display: grid; gap: 1rem; }
.two-column   { grid-template-columns: repeat(2, 1fr); }
.three-column { grid-template-columns: repeat(3, 1fr); }
@media (max-width: 820px) {
  .two-column, .three-column { grid-template-columns: 1fr; }
}

/* ---------- Callouts ---------- */
.callout {
  border: 1px solid var(--border);
  border-left-width: 5px;
  border-radius: 10px;
  padding: .95rem 1.1rem;
  margin: 1.1rem 0;
  background: var(--panel-2);
}
.callout > :first-child { margin-top: 0; }
.callout > :last-child  { margin-bottom: 0; }
.callout .callout-label {
  display: inline-block;
  font-size: .72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .09em;
  margin-bottom: .4rem;
}

.callout-key {
  border-left-color: var(--cyan);
  background: linear-gradient(180deg, rgba(52,211,224,.10), rgba(52,211,224,.02));
}
.callout-key .callout-label { color: var(--cyan); }

.callout-model {
  border-left-color: var(--violet);
  background: linear-gradient(180deg, rgba(157,139,255,.10), rgba(157,139,255,.02));
}
.callout-model .callout-label { color: var(--violet); }

.callout-warning {
  border-left-color: var(--amber);
  background: linear-gradient(180deg, rgba(244,180,69,.10), rgba(244,180,69,.02));
}
.callout-warning .callout-label { color: var(--amber); }

.callout-field {
  border-left-color: var(--green);
  background: linear-gradient(180deg, rgba(75,214,148,.10), rgba(75,214,148,.02));
}
.callout-field .callout-label { color: var(--green); }

/* ---------- Diagram (ASCII) ---------- */
.diagram {
  font-family: var(--mono);
  white-space: pre;
  overflow-x: auto;
  background: #08101d;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1.1rem;
  margin: 1.1rem 0;
  color: #bfe9ef;
  font-size: .86rem;
  line-height: 1.45;
  box-shadow: inset 0 0 0 1px rgba(52,211,224,.05);
}

/* ---------- Code ---------- */
code {
  font-family: var(--mono);
  background: #08101d;
  border: 1px solid var(--border-soft);
  border-radius: 5px;
  padding: .08em .4em;
  font-size: .88em;
  color: #cfe9ef;
}
pre {
  font-family: var(--mono);
  background: #08101d;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
  overflow-x: auto;
  color: #cfe9ef;
  font-size: .86rem;
}
pre code { background: none; border: none; padding: 0; }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; margin: 1.1rem 0; }
table {
  width: 100%;
  border-collapse: collapse;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  overflow: hidden;
  font-size: .92rem;
}
th, td {
  text-align: left;
  padding: .6rem .75rem;
  border-bottom: 1px solid var(--border-soft);
  vertical-align: top;
}
th {
  background: var(--panel-2);
  color: var(--cyan);
  font-weight: 600;
  white-space: nowrap;
}
tr:last-child td { border-bottom: none; }
tbody tr:hover { background: rgba(52,211,224,.04); }
td.num, th.num { text-align: right; font-family: var(--mono); white-space: nowrap; }
tfoot td { font-weight: 700; color: var(--text); background: var(--panel-2); }

/* ---------- Checklist ---------- */
.checklist {
  list-style: none;
  padding: 0;
  margin: 1rem 0;
}
.checklist li { margin: .35rem 0; }
.checklist label {
  display: flex;
  align-items: flex-start;
  gap: .6rem;
  cursor: pointer;
  padding: .5rem .7rem;
  background: var(--panel-2);
  border: 1px solid var(--border-soft);
  border-radius: 8px;
  color: var(--text-dim);
  transition: border-color .15s, background .15s;
}
.checklist label:hover { border-color: var(--cyan-deep); }
.checklist input.progress { margin-top: .25rem; width: 1.05rem; height: 1.05rem; accent-color: var(--cyan); flex: none; }
.checklist input.progress:checked + span,
.checklist label:has(input.progress:checked) { color: var(--text); }

/* ---------- Progress card ---------- */
.progress-card {
  background: linear-gradient(135deg, rgba(75,155,255,.10), rgba(52,211,224,.05)), var(--panel);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.4rem 1.5rem;
  margin: 1.2rem 0;
  box-shadow: var(--shadow);
}
.progress-card h2 { border: none; margin-top: 0; }

/* ---------- Term card (glossary) ---------- */
.term-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-left: 4px solid var(--cyan);
  border-radius: 8px;
  padding: .85rem 1rem;
  margin: .7rem 0;
}
.term-card h3 { margin: 0 0 .3rem; color: var(--text); font-size: 1.02rem; }
.term-card p { margin: 0; }

/* ---------- Badge ---------- */
.badge {
  display: inline-block;
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .05em;
  text-transform: uppercase;
  padding: .2rem .55rem;
  border-radius: 999px;
  background: rgba(52,211,224,.15);
  color: var(--cyan);
  border: 1px solid var(--cyan-deep);
  vertical-align: middle;
}
.badge.week   { background: rgba(75,155,255,.15); color: var(--blue); border-color: #2f5f9e; }
.badge.warn   { background: rgba(244,180,69,.15); color: var(--amber); border-color: #8a6c2c; }
.badge.ok     { background: rgba(75,214,148,.15); color: var(--green); border-color: #2f7e5b; }

/* ---------- Buttons ---------- */
.btn {
  display: inline-block;
  background: linear-gradient(180deg, var(--cyan), var(--cyan-deep));
  color: #04121a;
  font-weight: 700;
  text-decoration: none;
  padding: .7rem 1.3rem;
  border-radius: 9px;
  border: none;
  cursor: pointer;
  font-size: .98rem;
  transition: transform .1s, box-shadow .15s;
  box-shadow: 0 4px 14px rgba(52,211,224,.25);
}
.btn:hover { transform: translateY(-1px); box-shadow: 0 6px 18px rgba(52,211,224,.35); }
.btn-secondary {
  background: var(--panel);
  color: var(--text);
  border: 1px solid var(--border);
  box-shadow: none;
}

/* ---------- Collapsible review ---------- */
.collapsible { margin: 1rem 0; }
.collapsible-toggle {
  width: 100%;
  text-align: left;
  background: var(--panel-2);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: .65rem .9rem;
  cursor: pointer;
  font-size: .95rem;
  font-weight: 600;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.collapsible-toggle::after { content: "▸"; color: var(--cyan); transition: transform .15s; }
.collapsible-toggle.open::after { transform: rotate(90deg); }
.collapsible-body {
  display: none;
  padding: .8rem .95rem;
  border: 1px solid var(--border);
  border-top: none;
  border-radius: 0 0 8px 8px;
  background: var(--panel);
}
.collapsible-body.open { display: block; }

/* ---------- Show-answer ---------- */
.show-answer {
  background: var(--panel);
  color: var(--cyan);
  border: 1px solid var(--cyan-deep);
  border-radius: 7px;
  padding: .35rem .8rem;
  font-size: .85rem;
  font-weight: 600;
  cursor: pointer;
  margin: .4rem 0;
}
.show-answer:hover { background: rgba(52,211,224,.1); }
.answer {
  display: none;
  margin: .5rem 0 .2rem;
  padding: .7rem .9rem;
  background: rgba(75,214,148,.06);
  border: 1px solid #2f7e5b;
  border-radius: 8px;
  color: var(--text);
}
.answer.show { display: block; }

.qa { margin: .6rem 0; }
.qa .q { font-weight: 600; color: var(--text); margin-bottom: .2rem; }

/* ---------- Glossary search ---------- */
#glossary-search {
  width: 100%;
  padding: .7rem .9rem;
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: 9px;
  color: var(--text);
  font-size: 1rem;
  margin: 1rem 0;
}
#glossary-search::placeholder { color: var(--text-mute); }

/* ---------- Lesson nav ---------- */
.lesson-nav {
  max-width: var(--maxw);
  margin: 1.5rem auto 0;
  padding: 1rem 1.25rem;
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  border-top: 1px solid var(--border-soft);
}
.lesson-nav a {
  color: var(--text);
  text-decoration: none;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 9px;
  padding: .6rem 1rem;
  font-weight: 600;
  font-size: .92rem;
  transition: border-color .15s, background .15s;
}
.lesson-nav a:hover { border-color: var(--cyan); background: var(--panel-2); }
.lesson-nav a.next { margin-left: auto; }

/* ---------- Footer ---------- */
.site-footer {
  max-width: var(--maxw);
  margin: 2rem auto 1.5rem;
  padding: 1.2rem 1.25rem;
  color: var(--text-mute);
  font-size: .85rem;
  text-align: center;
  border-top: 1px solid var(--border-soft);
}

/* ---------- Responsive nav ---------- */
@media (max-width: 900px) {
  .nav-toggle { display: block; }
  .shell { display: block; }
  .sidebar {
    position: static;
    height: auto;
    overflow: visible;
    width: 100%;
    flex: none;
    padding: .6rem 1rem 1rem;
    border-right: none;
    border-bottom: 1px solid var(--border);
  }
  .nav-links { display: none; }
  .nav-links.open { display: flex; }
  .nav-group { margin-bottom: .55rem; }
  .nav-links a { padding: .55rem .7rem; font-size: .95rem; }
}