:root {
  --bg: #0B0E14;
  --surface: #121826;
  --surface-raised: #18202F;
  --border: #232C3F;
  --border-soft: #1B2333;
  --text-primary: #E4E8F1;
  --text-secondary: #8893A6;
  --text-dim: #5C6679;
  --amber: #F2B84B;
  --amber-dim: #7A5E2B;
  --green: #3DDC84;
  --green-dim: #1F5C3C;
  --slate: #3A4356;
  --danger: #E2645A;

  --font-mono: "IBM Plex Mono", ui-monospace, SFMono-Regular, monospace;
  --font-sans: "IBM Plex Sans", -apple-system, system-ui, sans-serif;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text-primary);
  font-family: var(--font-sans);
  height: 100%;
}

body {
  background-image:
    linear-gradient(180deg, rgba(255,255,255,0.015) 0px, transparent 1px);
  background-size: 100% 2px;
}

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

.accent-amber { color: var(--amber); }

button { font-family: var(--font-mono); cursor: pointer; }

/* ---------- Login ---------- */
.login-screen {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background:
    radial-gradient(circle at 50% 0%, rgba(242,184,75,0.06), transparent 60%),
    var(--bg);
  padding: 24px;
}

.login-panel {
  width: 100%;
  max-width: 380px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 32px 28px;
  position: relative;
}

.login-rack-tag {
  position: absolute;
  top: -11px;
  left: 24px;
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text-dim);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  padding: 2px 8px;
  border-radius: 3px;
}

.login-title {
  font-family: var(--font-mono);
  font-size: 19px;
  font-weight: 600;
  letter-spacing: -0.01em;
  margin: 0 0 6px;
}

.login-sub {
  color: var(--text-secondary);
  font-size: 13px;
  margin: 0 0 24px;
}

.field-label {
  display: block;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  margin: 16px 0 6px;
}

#login-form input[type="text"],
#login-form input[type="password"] {
  width: 100%;
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 14px;
  padding: 10px 12px;
  border-radius: 4px;
  outline: none;
  transition: border-color 0.15s;
}

#login-form input:focus {
  border-color: var(--amber);
}

.btn-primary {
  width: 100%;
  margin-top: 22px;
  background: var(--amber);
  color: #1A1404;
  border: none;
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.08em;
  padding: 11px;
  border-radius: 4px;
  transition: filter 0.15s;
}
.btn-primary:hover { filter: brightness(1.08); }
.btn-primary:focus-visible { outline: 2px solid var(--text-primary); outline-offset: 2px; }

.login-error {
  margin-top: 14px;
  color: var(--danger);
  font-family: var(--font-mono);
  font-size: 12px;
  background: rgba(226,100,90,0.08);
  border: 1px solid rgba(226,100,90,0.3);
  padding: 8px 10px;
  border-radius: 4px;
}

/* ---------- App shell ---------- */
.app {
  height: 100vh;
  display: flex;
  flex-direction: column;
}

.topbar {
  display: flex;
  align-items: center;
  gap: 28px;
  padding: 14px 22px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.brand {
  display: flex;
  align-items: center;
  gap: 9px;
  flex-shrink: 0;
}
.brand-mark { color: var(--amber); font-size: 16px; }
.brand-text {
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 14px;
  letter-spacing: -0.01em;
}

.progress-gauge {
  flex: 1;
  max-width: 320px;
}
.gauge-label {
  font-family: var(--font-mono);
  font-size: 10.5px;
  letter-spacing: 0.06em;
  color: var(--text-dim);
  margin-bottom: 5px;
}
.gauge-label #progress-count { color: var(--text-secondary); font-weight: 600; }
.gauge-track {
  height: 6px;
  background: var(--border-soft);
  border-radius: 3px;
  overflow: hidden;
  position: relative;
}
.gauge-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--green-dim), var(--green));
  border-radius: 3px;
  transition: width 0.3s ease;
}

.topbar-actions {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-left: auto;
}

.search-wrap { position: relative; }
#search-input {
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 13px;
  padding: 8px 12px;
  border-radius: 4px;
  width: 220px;
  outline: none;
}
#search-input:focus { border-color: var(--amber); }

.search-results {
  position: absolute;
  top: calc(100% + 6px);
  right: 0;
  width: 340px;
  background: var(--surface-raised);
  border: 1px solid var(--border);
  border-radius: 6px;
  max-height: 360px;
  overflow-y: auto;
  z-index: 50;
  box-shadow: 0 12px 30px rgba(0,0,0,0.5);
}
.search-result-item {
  padding: 10px 12px;
  border-bottom: 1px solid var(--border-soft);
  cursor: pointer;
}
.search-result-item:last-child { border-bottom: none; }
.search-result-item:hover { background: var(--surface); }
.search-result-module {
  font-family: var(--font-mono);
  font-size: 10px;
  color: var(--amber);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}
.search-result-title { font-size: 13.5px; font-weight: 600; margin: 2px 0; }
.search-result-summary { font-size: 12px; color: var(--text-secondary); }
.search-empty { padding: 14px 12px; color: var(--text-dim); font-size: 13px; }

.btn-ghost {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 11px;
  letter-spacing: 0.06em;
  padding: 8px 14px;
  border-radius: 4px;
  transition: all 0.15s;
}
.btn-ghost:hover { border-color: var(--text-secondary); color: var(--text-primary); }

/* ---------- Layout ---------- */
.layout {
  flex: 1;
  display: flex;
  overflow: hidden;
}

/* ---------- Rack (sidebar) ---------- */
.rack {
  width: 340px;
  flex-shrink: 0;
  overflow-y: auto;
  background: var(--bg);
  border-right: 1px solid var(--border);
  padding: 16px 12px 40px;
}

.chassis {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  margin-bottom: 10px;
  overflow: hidden;
}

.chassis-header {
  display: flex;
  align-items: baseline;
  gap: 9px;
  padding: 11px 13px;
  cursor: pointer;
  user-select: none;
  border-bottom: 1px solid transparent;
}
.chassis.open .chassis-header {
  border-bottom-color: var(--border);
}
.chassis-tag {
  font-family: var(--font-mono);
  font-size: 10px;
  color: var(--text-dim);
  letter-spacing: 0.05em;
  flex-shrink: 0;
}
.chassis-title {
  font-size: 13px;
  font-weight: 600;
  flex: 1;
  line-height: 1.3;
}
.chassis-meta {
  font-family: var(--font-mono);
  font-size: 10.5px;
  color: var(--text-dim);
  flex-shrink: 0;
}
.chassis-caret {
  color: var(--text-dim);
  font-size: 10px;
  transition: transform 0.15s;
  flex-shrink: 0;
}
.chassis.open .chassis-caret { transform: rotate(90deg); }

.chassis-body { display: none; }
.chassis.open .chassis-body { display: block; }

.ru-row {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 13px 9px 16px;
  cursor: pointer;
  border-top: 1px solid var(--border-soft);
  transition: background 0.1s;
}
.ru-row:hover { background: var(--surface-raised); }
.ru-row.active { background: var(--surface-raised); }
.ru-row.active .ru-title { color: var(--amber); }

.led {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--slate);
  flex-shrink: 0;
}
.led.done {
  background: var(--green);
  box-shadow: 0 0 6px rgba(61,220,132,0.7);
}
.led.current {
  background: var(--amber);
  box-shadow: 0 0 6px rgba(242,184,75,0.7);
}

.ru-title {
  font-size: 12.5px;
  line-height: 1.3;
  color: var(--text-secondary);
}
.ru-row.active .ru-title, .ru-row:hover .ru-title { color: var(--text-primary); }

/* ---------- Content ---------- */
.content {
  flex: 1;
  overflow-y: auto;
  padding: 36px 48px 80px;
}

.empty-state {
  height: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  color: var(--text-dim);
}
.empty-glyph { font-size: 38px; color: var(--border); margin-bottom: 14px; }
.empty-state h2 { font-size: 16px; color: var(--text-secondary); margin: 0 0 6px; font-weight: 600; }
.empty-state p { font-size: 13px; margin: 0; }

.lesson-view { max-width: 760px; }

.breadcrumb {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--text-dim);
  letter-spacing: 0.04em;
  margin-bottom: 14px;
  text-transform: uppercase;
}
.breadcrumb .accent-amber { text-transform: none; }

.lesson-title {
  font-size: 27px;
  font-weight: 700;
  letter-spacing: -0.01em;
  margin: 0 0 10px;
  line-height: 1.25;
}

.lesson-summary {
  font-size: 15px;
  color: var(--text-secondary);
  margin: 0 0 28px;
  line-height: 1.5;
}

.lesson-body {
  font-size: 15px;
  line-height: 1.7;
  color: var(--text-primary);
}
.lesson-body p { margin: 0 0 16px; }
.lesson-body strong { color: #FFFFFF; font-weight: 600; }
.lesson-body ul { margin: 0 0 16px; padding-left: 22px; }
.lesson-body li { margin-bottom: 8px; }
.lesson-body code {
  font-family: var(--font-mono);
  background: var(--surface-raised);
  border: 1px solid var(--border);
  padding: 1px 6px;
  border-radius: 3px;
  font-size: 13px;
  color: var(--amber);
}

.section-block {
  margin-top: 30px;
  padding-top: 22px;
  border-top: 1px solid var(--border);
}
.section-label {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  margin-bottom: 12px;
  text-transform: uppercase;
}

.commands-block {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 4px 0;
}
.command-line {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 8px 14px;
  font-family: var(--font-mono);
  font-size: 13px;
  border-bottom: 1px solid var(--border-soft);
}
.command-line:last-child { border-bottom: none; }
.command-prompt { color: var(--green); flex-shrink: 0; }
.command-text { color: var(--text-primary); word-break: break-word; }
.commands-empty { padding: 14px; color: var(--text-dim); font-size: 13px; font-family: var(--font-mono); }

.lab-block {
  background: rgba(242,184,75,0.06);
  border: 1px solid var(--amber-dim);
  border-radius: 6px;
  padding: 16px 18px;
  font-size: 14px;
  line-height: 1.6;
}
.lab-block-label {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--amber);
  letter-spacing: 0.08em;
  margin-bottom: 8px;
  display: block;
}

#notes-textarea {
  width: 100%;
  min-height: 110px;
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 13.5px;
  line-height: 1.5;
  padding: 12px 14px;
  border-radius: 6px;
  resize: vertical;
  outline: none;
}
#notes-textarea:focus { border-color: var(--text-dim); }
.notes-status {
  font-family: var(--font-mono);
  font-size: 10.5px;
  color: var(--text-dim);
  margin-top: 6px;
  height: 14px;
}

.lesson-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-top: 36px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

.complete-toggle {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 13px;
  font-weight: 600;
  padding: 10px 16px;
  border-radius: 5px;
  transition: all 0.15s;
}
.complete-toggle .led { width: 9px; height: 9px; }
.complete-toggle.is-done {
  border-color: var(--green-dim);
  color: var(--green);
  background: rgba(61,220,132,0.07);
}

.nav-buttons { display: flex; gap: 8px; }
.nav-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 12px;
  padding: 9px 14px;
  border-radius: 5px;
  max-width: 220px;
  text-align: left;
  font-family: var(--font-sans);
}
.nav-btn:hover { border-color: var(--text-dim); color: var(--text-primary); }
.nav-btn .nav-dir {
  display: block;
  font-family: var(--font-mono);
  font-size: 9.5px;
  color: var(--text-dim);
  letter-spacing: 0.06em;
  margin-bottom: 2px;
}
.nav-btn:disabled { opacity: 0.35; cursor: default; }
.nav-btn:disabled:hover { border-color: var(--border); color: var(--text-secondary); }

/* ---------- Scrollbars ---------- */
.rack::-webkit-scrollbar, .content::-webkit-scrollbar, .search-results::-webkit-scrollbar {
  width: 8px;
}
.rack::-webkit-scrollbar-thumb, .content::-webkit-scrollbar-thumb, .search-results::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}

/* ---------- Responsive ---------- */
@media (max-width: 880px) {
  .topbar { flex-wrap: wrap; gap: 12px; }
  .progress-gauge { order: 3; max-width: none; width: 100%; }
  .layout { flex-direction: column; overflow: visible; }
  .rack { width: 100%; max-height: 280px; border-right: none; border-bottom: 1px solid var(--border); }
  .content { padding: 26px 20px 60px; }
  #search-input { width: 150px; }
}

/* ---------- Reduced motion ---------- */
@media (prefers-reduced-motion: reduce) {
  .gauge-fill, .chassis-caret, .nav-btn, .btn-ghost, .btn-primary { transition: none; }
}