/* ------------------------------------------------------------------ tokens
   Maroon branding, quiet slate-blue controls, and a separate plot palette. */
:root {
  --bg: #f6f7f9;
  --surface: #ffffff;
  --surface-2: #eef1f4;
  --text: #16202a;
  --muted: #5b6875;
  --border: #d8dee5;
  --brand: #7a1f2b;
  --on-brand: #ffffff;
  --accent: #52677d;
  --accent-strong: #3c5269;
  --on-accent: #ffffff;
  --accent-soft: #edf1f5;
  --focus: #1d4ed8;
  --good: #15803d;
  --warn: #b45309;
  --bad: #b91c1c;
  /* plot palette (colour-blind safe, distinguishable in both themes) */
  --c1: #376d96;
  --c2: #c2410c;
  --c3: #7c3aed;
  --c4: #15803d;
  --c5: #be185d;
  --grid: #e3e8ee;
  --grid-strong: #c4ccd6;
  --axis: #3b4754;
  --plot-bg: #ffffff;
  --shadow: 0 1px 2px rgba(15, 23, 42, 0.06), 0 6px 20px rgba(15, 23, 42, 0.06);
  --radius: 10px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0f1418;
    --surface: #182027;
    --surface-2: #212b34;
    --text: #e6ebf0;
    --muted: #9aa8b5;
    --border: #2d3944;
    --brand: #e0838f;
    --on-brand: #2b080d;
    --accent: #9bb6ce;
    --accent-strong: #c0d2e2;
    --on-accent: #122334;
    --accent-soft: #263542;
    --focus: #7aa2ff;
    --good: #4ade80;
    --warn: #fbbf24;
    --bad: #f87171;
    --c1: #83b6dc;
    --c2: #fb923c;
    --c3: #a78bfa;
    --c4: #4ade80;
    --c5: #f472b6;
    --grid: #26313b;
    --grid-strong: #3a4753;
    --axis: #b6c2ce;
    --plot-bg: #131a20;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 6px 20px rgba(0, 0, 0, 0.35);
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0f1418;
  --surface: #182027;
  --surface-2: #212b34;
  --text: #e6ebf0;
  --muted: #9aa8b5;
  --border: #2d3944;
  --brand: #e0838f;
  --on-brand: #2b080d;
  --accent: #9bb6ce;
  --accent-strong: #c0d2e2;
  --on-accent: #122334;
  --accent-soft: #263542;
  --focus: #7aa2ff;
  --good: #4ade80;
  --warn: #fbbf24;
  --bad: #f87171;
  --c1: #83b6dc;
  --c2: #fb923c;
  --c3: #a78bfa;
  --c4: #4ade80;
  --c5: #f472b6;
  --grid: #26313b;
  --grid-strong: #3a4753;
  --axis: #b6c2ce;
  --plot-bg: #131a20;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 6px 20px rgba(0, 0, 0, 0.35);
  color-scheme: dark;
}

/* ------------------------------------------------------------------- base */
* {
  box-sizing: border-box;
}
html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 76px;
}
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font:
    15px/1.55 system-ui,
    -apple-system,
    "Segoe UI",
    Roboto,
    "Helvetica Neue",
    Arial,
    sans-serif;
}
button,
input,
select {
  font: inherit;
  color: inherit;
}
button {
  cursor: pointer;
}
a {
  color: var(--accent-strong);
}
:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
  border-radius: 4px;
}
.skip {
  position: absolute;
  left: -999px;
  top: 8px;
  background: var(--surface);
  padding: 8px 12px;
  border-radius: 6px;
  z-index: 50;
}
.skip:focus {
  left: 8px;
}
h1,
h2,
h3,
h4,
p {
  margin: 0;
}
.katex {
  font-size: 1.05em;
}
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  * {
    transition: none !important;
    animation: none !important;
  }
}

/* ----------------------------------------------------------------- header */
.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 20px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 30;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
}
.brand-link {
  display: flex;
  align-items: center;
  gap: 12px;
  color: inherit;
  text-decoration: none;
  min-width: 0;
}
.logo {
  color: var(--brand);
  display: grid;
}
.brand h1,
.hero h2,
.page-head h2 {
  color: var(--brand);
}
.brand h1 {
  font-size: 17px;
  line-height: 1.2;
  font-weight: 650;
  letter-spacing: -0.01em;
}
.tag {
  font-size: 12.5px;
  color: var(--muted);
}
.header-tools {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-shrink: 0;
}
.icon-btn {
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  border-radius: 8px;
  background: var(--surface-2);
  border: 1px solid var(--border);
}
.icon-btn:hover {
  border-color: var(--accent);
}
.fb-btn {
  width: auto;
  display: flex;
  gap: 6px;
  padding: 0 12px;
  font-size: 13px;
  color: inherit;
  text-decoration: none;
  align-items: center;
}
.menu-btn {
  display: none;
}
.i-sun {
  display: none;
}
:root[data-theme="dark"] .i-sun {
  display: block;
}
:root[data-theme="dark"] .i-moon {
  display: none;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .i-sun {
    display: block;
  }
  :root:not([data-theme="light"]) .i-moon {
    display: none;
  }
}

/* segmented control (also used inside lessons) */
.seg {
  display: inline-flex;
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 2px;
  gap: 2px;
  flex-wrap: wrap;
  max-width: 100%;
}
.seg button {
  border: 0;
  background: transparent;
  padding: 6px 12px;
  border-radius: 6px;
  color: var(--muted);
  font-weight: 550;
  min-height: 32px;
}
.seg button:hover {
  color: var(--text);
}
.seg button[aria-pressed="true"] {
  background: var(--accent);
  color: var(--on-accent);
}

/* ----------------------------------------------------------------- layout */
.layout {
  display: grid;
  grid-template-columns: minmax(260px, 320px) minmax(0, 1fr);
  gap: 20px;
  padding: 20px;
  max-width: 1500px;
  margin: 0 auto;
  align-items: start;
}
.sidebar {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
  position: sticky;
  top: 68px;
  max-height: calc(100vh - 88px);
  display: flex;
  flex-direction: column;
  min-height: 0;
}
.side-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 8px;
}
.side-head h2 {
  font-size: 15px;
  font-weight: 650;
}
.count {
  font-size: 12.5px;
  color: var(--accent-strong);
  font-weight: 600;
}
.search {
  width: 100%;
  padding: 8px 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg);
}
.side-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 4px 14px;
  margin: 8px 0 6px;
}
.link-btn {
  border: 0;
  background: none;
  padding: 2px 0;
  color: var(--accent-strong);
  font-size: 12.5px;
  font-weight: 600;
}
.link-btn:hover {
  text-decoration: underline;
}
.main {
  min-width: 0;
  outline: none;
}

/* sidebar tree */
.tree {
  overflow: auto;
  margin: 0 -6px;
  padding: 0 6px;
  flex: 1;
  min-height: 0;
}
.tree details {
  margin: 0;
}
.tree summary {
  list-style: none;
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 5px 4px;
  border-radius: 6px;
  cursor: pointer;
  user-select: none;
}
.tree summary::-webkit-details-marker {
  display: none;
}
.tree summary:hover {
  background: var(--surface-2);
}
.tree summary::before {
  content: "";
  width: 7px;
  height: 7px;
  border-right: 2px solid var(--muted);
  border-bottom: 2px solid var(--muted);
  transform: rotate(-45deg);
  transition: transform 0.12s;
  margin: 0 4px 0 2px;
  flex-shrink: 0;
}
.tree details[open] > summary::before {
  transform: rotate(45deg);
}
.tree .form-sum {
  font-weight: 650;
  font-size: 14px;
}
.tree .form-body {
  margin-left: 8px;
  border-left: 1px solid var(--border);
  padding-left: 6px;
}
.tree a.row {
  display: flex;
  align-items: flex-start;
  gap: 7px;
  padding: 4px 6px;
  border-radius: 6px;
  font-size: 13.5px;
  line-height: 1.35;
  color: var(--text);
  text-decoration: none;
}
.tree a.row:hover {
  background: var(--surface-2);
}
.tree a.row[aria-current="page"] {
  background: var(--accent-soft);
  color: var(--accent-strong);
  font-weight: 600;
}
.tree .no {
  color: var(--muted);
  font-variant-numeric: tabular-nums;
  min-width: 1.6em;
  flex-shrink: 0;
}
.tree .secs {
  margin: 0 0 4px 30px;
  display: grid;
  gap: 1px;
  border-left: 1px solid var(--border);
  padding-left: 8px;
}
.tree .secs a {
  font-size: 12.5px;
  color: var(--muted);
  text-decoration: none;
  padding: 2px 4px;
  border-radius: 4px;
  line-height: 1.35;
}
.tree .secs a:hover {
  color: var(--text);
  background: var(--surface-2);
}
.tree .empty {
  color: var(--muted);
  font-size: 13px;
  padding: 8px 4px;
}
.tree .hide {
  display: none;
}
.badge {
  font-size: 10.5px;
  padding: 0 6px;
  border-radius: 99px;
  border: 1px solid var(--border);
  color: var(--muted);
  white-space: nowrap;
}
.scrim {
  display: none;
}

/* ------------------------------------------------------------------ pages */
.page-head {
  margin-bottom: 16px;
}
.crumbs {
  font-size: 12.5px;
  color: var(--muted);
  margin-bottom: 4px;
}
.crumbs a {
  color: var(--muted);
  text-decoration: none;
}
.crumbs a:hover {
  text-decoration: underline;
}
.page-head h2 {
  font-size: 26px;
  line-height: 1.2;
  letter-spacing: -0.015em;
  font-weight: 700;
}
.lede {
  color: var(--muted);
  font-size: 15.5px;
  margin-top: 6px;
  max-width: 70ch;
}
.chapter-nav {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  margin-top: 18px;
  flex-wrap: wrap;
}
.chapter-nav a {
  display: inline-flex;
  flex-direction: column;
  gap: 2px;
  padding: 10px 14px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  text-decoration: none;
  color: var(--text);
  max-width: 48%;
}
.chapter-nav a:hover {
  border-color: var(--accent);
}
.chapter-nav small {
  color: var(--muted);
  font-size: 12px;
}
.chapter-nav .next {
  text-align: right;
  margin-left: auto;
}

.sec {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 20px;
  margin-bottom: 16px;
  box-shadow: var(--shadow);
}
.sec > h3 {
  font-size: 18px;
  font-weight: 650;
  letter-spacing: -0.01em;
  margin-bottom: 6px;
}
.sec p {
  margin: 8px 0;
  max-width: 78ch;
}
.sec .std {
  display: inline-block;
  font-size: 11.5px;
  color: var(--muted);
  border: 1px solid var(--border);
  border-radius: 99px;
  padding: 0 8px;
  margin-left: 8px;
  vertical-align: middle;
  font-weight: 500;
}

.callout {
  border-left: 4px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 0 8px 8px 0;
  padding: 10px 14px;
  margin: 12px 0;
  max-width: 78ch;
}
.callout.warn {
  border-left-color: var(--warn);
  background: color-mix(in srgb, var(--warn) 12%, var(--surface));
}
.callout.good {
  border-left-color: var(--good);
  background: color-mix(in srgb, var(--good) 12%, var(--surface));
}
.callout > b:first-child {
  display: block;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent-strong);
  margin-bottom: 2px;
}
.callout.warn > b:first-child {
  color: var(--warn);
}
.callout.good > b:first-child {
  color: var(--good);
}
.callout p {
  margin: 4px 0;
}
.formula {
  padding: 8px 12px;
  background: var(--surface-2);
  border-radius: 8px;
  margin: 10px 0;
  overflow-x: auto;
  max-width: 100%;
}

/* ---------------------------------------------------- interactive widgets */
.lab {
  display: grid;
  grid-template-columns: minmax(0, 1.55fr) minmax(250px, 1fr);
  gap: 16px;
  align-items: start;
  margin: 12px 0;
}
.lab.stack {
  grid-template-columns: minmax(0, 1fr);
}
.lab.sticky > .panel {
  position: sticky;
  top: 76px;
  max-height: calc(100vh - 92px);
  overflow-y: auto;
  gap: 4px;
}
/* the sticky panel is narrow, so long slider labels sit on their own line instead of squeezing the slider */
.lab.sticky .param {
  row-gap: 0;
}
.lab.sticky .param label {
  grid-column: 1 / -1;
  font-size: 13.5px;
}
.lab.sticky .param input[type="number"] {
  padding: 2px 6px;
}
.lab.sticky .param input[type="range"] {
  grid-column: 1 / 3;
}
.mini-bar {
  display: none;
}
.lab > * {
  min-width: 0;
}
.panel {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px 14px;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 10px;
  align-content: start;
}
.panel h4 {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--muted);
  font-weight: 650;
}
.plot-wrap {
  position: relative;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  background: var(--plot-bg);
  touch-action: pan-y;
}
.plot-wrap svg {
  display: block;
  width: 100%;
  height: auto;
  user-select: none;
  -webkit-user-select: none;
}
.plot-wrap.draggable svg {
  touch-action: none;
}
.plot-tools {
  position: absolute;
  right: 6px;
  top: 6px;
  display: flex;
  gap: 4px;
}
.plot-tools button {
  width: 28px;
  height: 28px;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  display: grid;
  place-items: center;
  font-weight: 700;
  line-height: 1;
  opacity: 0.85;
}
.plot-tools button:hover {
  border-color: var(--accent);
  opacity: 1;
}
.plot-cap {
  font-size: 12.5px;
  color: var(--muted);
  margin-top: 6px;
}
.plot-hint {
  position: absolute;
  left: 8px;
  bottom: 6px;
  font-size: 11px;
  color: var(--muted);
  pointer-events: none;
  background: color-mix(in srgb, var(--plot-bg) 80%, transparent);
  padding: 0 4px;
  border-radius: 4px;
}
.handle {
  cursor: grab;
}
.handle:active {
  cursor: grabbing;
}

.param {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) 5.2em;
  gap: 8px;
  align-items: center;
}
.param label {
  font-weight: 600;
  min-width: 1.4em;
}
.param input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
  min-height: 28px;
}
.param input[type="number"] {
  width: 100%;
  padding: 4px 6px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  text-align: right;
  font-variant-numeric: tabular-nums;
}
.field {
  display: grid;
  gap: 4px;
}
.field > label,
.field > .lbl {
  font-size: 12.5px;
  font-weight: 600;
  color: var(--muted);
}
.field input[type="text"],
.field input[type="number"],
.field select {
  width: 100%;
  padding: 7px 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
}
.field input.bad {
  border-color: var(--bad);
}
.field .err {
  color: var(--bad);
  font-size: 12.5px;
  min-height: 1.2em;
}
.row-wrap {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  align-items: center;
}
.check {
  display: flex;
  gap: 8px;
  align-items: center;
  font-size: 14px;
  cursor: pointer;
}
.check input {
  accent-color: var(--accent);
  width: 16px;
  height: 16px;
}
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 7px 14px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  font-weight: 600;
  min-height: 36px;
}
.btn:hover {
  border-color: var(--accent);
}
.btn.primary {
  background: var(--accent);
  color: var(--on-accent);
  border-color: var(--accent);
}
.chips {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}
.chip {
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: 99px;
  padding: 3px 10px;
  font-size: 13px;
}
.chip:hover {
  border-color: var(--accent);
}
.chip[aria-pressed="true"] {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent-strong);
  font-weight: 600;
}

.readout {
  display: grid;
  gap: 4px;
  font-variant-numeric: tabular-nums;
}
.readout .r {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  align-items: baseline;
  padding: 3px 0;
  border-bottom: 1px dashed var(--border);
}
.readout .r:last-child {
  border-bottom: 0;
}
.readout .k {
  color: var(--muted);
  font-size: 13px;
}
.readout .v {
  font-weight: 650;
  text-align: right;
}
.eq-display {
  font-size: 1.15em;
  padding: 6px 2px;
  overflow-x: auto;
}
.swatch {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 3px;
  margin-right: 6px;
  vertical-align: -1px;
}
.tbl {
  border-collapse: collapse;
  font-variant-numeric: tabular-nums;
  max-width: 100%;
}
.tbl th,
.tbl td {
  border: 1px solid var(--border);
  padding: 4px 10px;
  text-align: center;
}
.tbl th {
  background: var(--surface-2);
  font-weight: 600;
}
.tbl-wrap {
  overflow-x: auto;
  max-width: 100%;
}
.tag-good {
  color: var(--good);
  font-weight: 650;
}
.tag-bad {
  color: var(--bad);
  font-weight: 650;
}

/* mini quiz */
.quiz {
  border: 1px dashed var(--border);
  border-radius: 8px;
  padding: 12px 14px;
  margin: 14px 0 4px;
  background: color-mix(in srgb, var(--accent-soft) 40%, var(--surface));
}
.quiz h4 {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent-strong);
  margin-bottom: 6px;
}
.quiz .q {
  margin-bottom: 8px;
}
.quiz .opts {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.quiz .opts button {
  padding: 6px 14px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  min-height: 36px;
}
.quiz .opts button:hover:not(:disabled) {
  border-color: var(--accent);
}
.quiz .opts button.right {
  border-color: var(--good);
  background: color-mix(in srgb, var(--good) 15%, var(--surface));
}
.quiz .opts button.wrong {
  border-color: var(--bad);
  background: color-mix(in srgb, var(--bad) 12%, var(--surface));
}
.quiz .fb {
  margin-top: 8px;
  font-size: 14px;
  min-height: 1.4em;
}
.quiz .ans-row {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}
.quiz .ans-row input {
  padding: 7px 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  width: 10em;
}

/* home */
.hero {
  background: linear-gradient(135deg, var(--accent-soft), var(--surface));
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 26px 24px;
  margin-bottom: 20px;
}
.hero h2 {
  font-size: 30px;
  letter-spacing: -0.02em;
  line-height: 1.15;
}
.hero p {
  margin-top: 8px;
  max-width: 62ch;
  color: var(--muted);
  font-size: 16px;
}
.hero svg {
  max-width: 100%;
  height: auto;
  margin-top: 14px;
}
.form-block {
  margin-bottom: 22px;
}
.form-block > h3 {
  font-size: 18px;
  margin-bottom: 8px;
}
.cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(230px, 1fr));
  gap: 10px;
}
.card {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 12px 14px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  color: var(--text);
  text-decoration: none;
}
.card:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow);
}
.card .n {
  font-size: 12px;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}
.card .t {
  font-weight: 600;
  line-height: 1.3;
}
.card .d {
  font-size: 13px;
  color: var(--muted);
}
.soon {
  opacity: 0.6;
}
.prose h3 {
  margin-top: 18px;
}
.prose ul {
  padding-left: 20px;
  max-width: 78ch;
}

.loading,
.errbox {
  padding: 30px;
  text-align: center;
  color: var(--muted);
}

/* sister-site links inside the drawer (header buttons are hidden on phones) */
.side-links {
  display: none;
  gap: 16px;
  padding-top: 10px;
  margin-top: 8px;
  border-top: 1px solid var(--border);
  font-size: 13px;
}

/* --------------------------------------------------------------- responsive */
@media (max-width: 1000px) {
  .lab {
    grid-template-columns: minmax(0, 1fr);
  }
  .lab.sticky > .panel {
    position: static;
    max-height: none;
    overflow: visible;
  }
  .mini-bar {
    display: grid;
    grid-template-columns: auto auto;
    justify-content: space-between;
    gap: 2px 10px;
    position: sticky;
    bottom: 0;
    margin: 4px -14px -12px;
    padding: 8px 14px;
    background: var(--surface);
    border-top: 2px solid var(--accent);
    border-radius: 0 0 8px 8px;
    box-shadow: 0 -4px 12px rgba(0, 0, 0, 0.08);
    font-size: 13.5px;
    font-variant-numeric: tabular-nums;
  }
  .mini-bar span {
    color: var(--muted);
  }
  .mini-bar b {
    text-align: right;
  }
}
@media (max-width: 900px) {
  .layout {
    grid-template-columns: minmax(0, 1fr);
    padding: 12px 16px;
  }
  .menu-btn {
    display: grid;
  }
  .sidebar {
    position: fixed;
    z-index: 40;
    left: 0;
    top: 0;
    bottom: 0;
    width: min(340px, 88vw);
    max-height: none;
    border-radius: 0 var(--radius) var(--radius) 0;
    transform: translateX(-102%);
    transition: transform 0.18s;
  }
  body.nav-open .sidebar {
    transform: none;
  }
  body.nav-open .scrim {
    display: block;
    position: fixed;
    inset: 0;
    z-index: 35;
    background: rgba(0, 0, 0, 0.45);
  }
  .app-header {
    padding: 8px 16px;
  }
}
@media (max-width: 760px) {
  .fb-btn span {
    display: none;
  }
  .fb-btn {
    padding: 0;
    width: 36px;
    justify-content: center;
  }
  .tag {
    display: none;
  }
  .page-head h2 {
    font-size: 22px;
  }
}
@media (max-width: 520px) {
  .fb-btn.sister {
    display: none;
  }
  .side-links {
    display: flex;
  }
  .brand h1 {
    font-size: 14px;
  }
  .brand,
  .brand-link,
  .header-tools {
    gap: 6px;
  }
  .seg button {
    padding: 6px 9px;
  }
  .app-header {
    padding: 8px 10px;
    gap: 6px;
  }
  .sec {
    padding: 14px 14px;
  }
  .param {
    grid-template-columns: auto minmax(0, 1fr) 4.6em;
  }
}
@media (max-width: 420px) {
  .header-tools {
    gap: 5px;
  }
  .header-tools .seg button {
    padding: 6px 8px;
  }
}
@media (max-width: 400px) {
  .brand h1 {
    font-size: 13px;
  }
  .icon-btn {
    width: 32px;
    height: 32px;
  }
  .fb-btn {
    width: 32px;
  }
}
@media (max-width: 340px) {
  .brand h1 {
    font-size: 11.5px;
  }
  .seg button {
    padding: 6px 7px;
  }
}