:root {
  color-scheme: dark;
  --bg: #0f172a;
  --surface: #1e293b;
  --surface-2: #26344a;
  --border: #334155;
  --border-strong: #475569;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-soft: rgb(56 189 248 / 0.14);
  --accent-ink: #082032;
  --danger: #f87171;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 1px 2px rgb(2 6 23 / 0.4), 0 8px 24px rgb(2 6 23 / 0.28);
  --fast: 150ms ease;
  --slow: 250ms ease;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", "Cascadia Mono", Menlo, Consolas, monospace;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
}

body {
  margin: 0;
  min-height: 100vh;
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
  background: var(--bg);
  color: var(--text);
  font: 15px/1.5 var(--font);
}

button,
input,
select {
  font: inherit;
  color: inherit;
}

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

.icon {
  width: 18px;
  height: 18px;
  flex: none;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

/* ---------- header and footer ---------- */

.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 8px 16px;
  border-bottom: 1px solid var(--border);
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
  margin: 0;
  font-size: 1.125rem;
  font-weight: 650;
  letter-spacing: -0.01em;
  white-space: nowrap;
}

.brand span {
  overflow: hidden;
  text-overflow: ellipsis;
}

.brand-mark {
  width: 30px;
  height: 30px;
  flex: none;
}

.header-actions {
  display: flex;
  flex: none;
  gap: 8px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  min-width: 40px;
  min-height: 40px;
  padding: 0 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  font-size: 0.875rem;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--fast), border-color var(--fast), color var(--fast), transform var(--fast);
}

.btn:hover:not(:disabled) {
  background: var(--surface-2);
  border-color: var(--border-strong);
}

.btn:active:not(:disabled) {
  transform: translateY(1px);
}

.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.btn-lang {
  min-width: 48px;
  padding: 0 10px;
  color: var(--accent);
  letter-spacing: 0.04em;
}

.btn-accent {
  border-color: transparent;
  background: var(--accent);
  color: var(--accent-ink);
}

.btn-accent:hover:not(:disabled) {
  border-color: transparent;
  background: #7dd3fc;
}

.btn-small {
  padding: 0 12px 0 10px;
}

.app-footer {
  padding: 4px 16px 12px;
  text-align: center;
  font-size: 0.8125rem;
}

.app-footer a {
  display: inline-flex;
  align-items: center;
  min-height: 40px;
  padding: 0 8px;
  color: var(--muted);
  text-decoration: none;
  transition: color var(--fast);
}

.app-footer a:hover {
  color: var(--accent);
  text-decoration: underline;
}

/* ---------- layout ---------- */

.app-main {
  flex: 1;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  align-content: start;
  gap: 12px;
  padding: 12px;
}

.plot {
  position: relative;
  height: min(60vh, 520px);
  min-height: 280px;
  overflow: hidden;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg);
  box-shadow: var(--shadow);
}

#plot {
  position: absolute;
  inset: 0;
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
  cursor: crosshair;
}

#plot.is-dragging {
  cursor: grabbing;
}

#plot:focus-visible {
  outline-offset: -3px;
}

.panel {
  display: flex;
  flex-direction: column;
  gap: 10px;
  min-width: 0;
}

@media (min-width: 900px) {
  body {
    height: 100vh;
    height: 100dvh;
    min-height: 560px;
  }

  .app-main {
    grid-template-columns: minmax(0, 1fr) 340px;
    grid-template-rows: minmax(0, 1fr);
    align-content: stretch;
    gap: 16px;
    min-height: 0;
    padding: 16px 16px 8px;
  }

  .plot {
    height: auto;
    min-height: 0;
  }

  .app-footer {
    padding: 0 16px 4px;
  }

  .app-footer a {
    min-height: 32px;
  }

  .panel {
    min-height: 0;
    overflow-y: auto;
    padding-right: 4px;
    margin-right: -4px;
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
  }
}

/* ---------- plot overlays ---------- */

.zoom-controls {
  position: absolute;
  right: 10px;
  bottom: 10px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  flex: none;
  padding: 0;
  border: 1px solid transparent;
  border-radius: var(--radius);
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  transition: background var(--fast), color var(--fast), border-color var(--fast);
}

.icon-btn:hover {
  background: var(--surface-2);
  color: var(--text);
}

.zoom-controls .icon-btn {
  border-color: var(--border);
  background: rgb(30 41 59 / 0.92);
  color: var(--text);
  box-shadow: var(--shadow);
}

.zoom-controls .icon-btn:hover {
  border-color: var(--border-strong);
  background: var(--surface-2);
}

.plot-hint {
  position: absolute;
  top: 12px;
  left: 50%;
  width: max-content;
  max-width: calc(100% - 24px);
  margin: 0;
  padding: 6px 14px;
  transform: translateX(-50%);
  border: 1px solid var(--border);
  border-radius: 999px;
  background: rgb(30 41 59 / 0.92);
  color: var(--muted);
  font-size: 0.8125rem;
  text-align: center;
  pointer-events: none;
  transition: opacity var(--slow);
}

.plot-hint.is-faded {
  opacity: 0;
}

/* ---------- cards ---------- */

.card {
  padding: 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: var(--shadow);
}

.card h2,
.card > summary {
  margin: 0;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.card-head {
  display: flex;
  align-items: center;
  gap: 8px;
  min-height: 40px;
  margin: -6px 0 0;
}

.card-head h2 {
  margin-right: auto;
}

.count {
  color: var(--muted);
  font-size: 0.8125rem;
  font-variant-numeric: tabular-nums;
}

details.card > summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 40px;
  margin: -8px 0;
  list-style: none;
  cursor: pointer;
  transition: color var(--fast);
}

details.card > summary::-webkit-details-marker {
  display: none;
}

details.card > summary::after {
  content: "";
  width: 7px;
  height: 7px;
  margin: 0 4px 3px 0;
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: rotate(45deg);
  transition: transform var(--fast);
}

details.card[open] > summary {
  margin-bottom: 0;
}

details.card[open] > summary::after {
  margin-bottom: -3px;
  transform: rotate(225deg);
}

details.card > summary:hover {
  color: var(--text);
}

/* ---------- inputs ---------- */

.fn-input,
.field input,
.field select {
  width: 100%;
  min-width: 0;
  min-height: 40px;
  padding: 8px 10px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg);
  font: 16px/1.2 var(--mono);
  transition: border-color var(--fast), box-shadow var(--fast);
}

.fn-input:focus,
.field input:focus,
.field select:focus {
  border-color: var(--accent);
  outline: none;
  box-shadow: 0 0 0 3px var(--accent-soft);
}

.fn-input[aria-invalid="true"],
.field input[aria-invalid="true"] {
  border-color: var(--danger);
  box-shadow: 0 0 0 3px rgb(248 113 113 / 0.14);
}

.fn-input::placeholder {
  color: #64748b;
}

.field select {
  appearance: none;
  padding-right: 34px;
  background: var(--bg)
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%2394a3b8' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M6 9l6 6 6-6'/%3E%3C/svg%3E")
    no-repeat right 10px center / 16px;
  font-family: var(--font);
  text-overflow: ellipsis;
  cursor: pointer;
}

.field select:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.field-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
  margin-top: 10px;
}

.field {
  display: grid;
  gap: 4px;
  min-width: 0;
  color: var(--muted);
  font-size: 0.8125rem;
}

.int-fields {
  grid-template-columns: minmax(0, 1.5fr) repeat(2, minmax(0, 1fr));
}

.field-msg {
  margin: 8px 0 0;
  color: var(--danger);
  font-size: 0.8125rem;
}

/* ---------- function list ---------- */

.fn-list {
  display: grid;
  gap: 8px;
  margin: 8px 0 0;
  padding: 0;
  list-style: none;
}

.fn-row {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) 40px 40px;
  align-items: center;
  column-gap: 4px;
}

.fn-label {
  display: flex;
  align-items: center;
  gap: 8px;
  padding-right: 4px;
}

.fn-dot {
  display: inline-block;
  width: 10px;
  height: 10px;
  flex: none;
  border: 2px solid var(--fn);
  border-radius: 50%;
  background: var(--fn);
  box-shadow: 0 0 10px color-mix(in srgb, var(--fn) 45%, transparent);
  transition: background var(--fast), box-shadow var(--fast);
}

.fn-name {
  min-width: 34px;
  color: var(--muted);
  font: 0.9375rem var(--mono);
  white-space: nowrap;
}

.fn-row .fn-input:focus {
  border-color: var(--fn);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--fn) 18%, transparent);
}

.fn-row.is-hidden .fn-dot {
  background: transparent;
  box-shadow: none;
}

.fn-row.is-hidden .fn-input {
  color: var(--muted);
}

.fn-msg,
.fn-deriv {
  grid-column: 2 / -1;
  margin: 4px 0 0;
  font-size: 0.8125rem;
}

.fn-msg {
  color: var(--danger);
}

.fn-deriv {
  overflow: hidden;
  color: var(--muted);
  font-family: var(--mono);
  text-overflow: ellipsis;
  white-space: nowrap;
}

.fn-empty {
  padding: 12px;
  border: 1px dashed var(--border);
  border-radius: var(--radius-sm);
  color: var(--muted);
  font-size: 0.875rem;
  text-align: center;
}

/* ---------- parameters ---------- */

.param-list {
  display: grid;
  gap: 2px;
  margin-top: 6px;
}

.param-row {
  display: grid;
  grid-template-columns: 22px minmax(0, 1fr) 52px;
  align-items: center;
  gap: 10px;
}

.param-name {
  color: var(--accent);
  font: 600 1rem var(--mono);
  text-align: center;
}

.param-value {
  color: var(--text);
  font: 0.875rem var(--mono);
  font-variant-numeric: tabular-nums;
  text-align: right;
}

input[type="range"] {
  width: 100%;
  height: 40px;
  margin: 0;
  background: transparent;
  cursor: pointer;
  appearance: none;
}

input[type="range"]::-webkit-slider-runnable-track {
  height: 6px;
  border-radius: 3px;
  background: var(--border);
}

input[type="range"]::-webkit-slider-thumb {
  width: 20px;
  height: 20px;
  margin-top: -7px;
  border: 3px solid var(--surface);
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 1px var(--accent);
  appearance: none;
  transition: transform var(--fast);
}

input[type="range"]:active::-webkit-slider-thumb {
  transform: scale(1.15);
}

input[type="range"]::-moz-range-track {
  height: 6px;
  border-radius: 3px;
  background: var(--border);
}

input[type="range"]::-moz-range-progress {
  height: 6px;
  border-radius: 3px;
  background: var(--accent);
}

input[type="range"]::-moz-range-thumb {
  width: 14px;
  height: 14px;
  border: 3px solid var(--surface);
  border-radius: 50%;
  background: var(--accent);
}

input[type="range"]:focus-visible {
  outline-offset: 0;
}

/* ---------- toggles ---------- */

.chips {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
  margin-top: 10px;
}

.chip {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-width: 0;
  min-height: 40px;
  padding: 0 12px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: transparent;
  color: var(--muted);
  font-size: 0.875rem;
  font-weight: 600;
  text-align: left;
  cursor: pointer;
  transition: background var(--fast), border-color var(--fast), color var(--fast);
}

.chip::before {
  content: "";
  width: 10px;
  height: 10px;
  flex: none;
  border: 2px solid currentColor;
  border-radius: 50%;
  transition: background var(--fast), border-color var(--fast);
}

.chip:hover {
  border-color: var(--border-strong);
  color: var(--text);
}

.chip[aria-pressed="true"] {
  border-color: rgb(56 189 248 / 0.55);
  background: var(--accent-soft);
  color: var(--text);
}

.chip[aria-pressed="true"]::before {
  border-color: var(--accent);
  background: var(--accent);
}

.switch {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: flex-end;
  min-width: 52px;
  min-height: 40px;
  cursor: pointer;
}

.switch input {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  margin: 0;
  opacity: 0;
  cursor: pointer;
}

.switch-track {
  position: relative;
  width: 44px;
  height: 24px;
  border-radius: 999px;
  background: var(--border);
  transition: background var(--fast);
}

.switch-track::after {
  content: "";
  position: absolute;
  top: 3px;
  left: 3px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--text);
  transition: transform var(--fast), background var(--fast);
}

.switch input:checked + .switch-track {
  background: var(--accent);
}

.switch input:checked + .switch-track::after {
  transform: translateX(20px);
  background: var(--accent-ink);
}

.switch input:focus-visible + .switch-track {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ---------- integral ---------- */

.int-result {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  min-height: 44px;
  margin: 10px 0 0;
  padding: 8px 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg);
  font: 0.9375rem var(--mono);
}

.int-result.is-muted {
  color: var(--muted);
  font: 0.8125rem var(--font);
}

.int-sign {
  margin-right: 1px;
  font-size: 1.5rem;
  line-height: 1;
}

.int-bounds {
  display: inline-flex;
  flex-direction: column;
  margin-right: 4px;
  font-size: 0.6875rem;
  line-height: 1.15;
}

.int-bounds sup,
.int-bounds sub {
  position: static;
  font-size: inherit;
  vertical-align: baseline;
}

.int-result strong {
  margin-left: 6px;
  font-weight: 700;
}

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

.table-scroll {
  margin-top: 12px;
  overflow-x: auto;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
}

.values {
  width: 100%;
  border-collapse: collapse;
  font: 0.8125rem var(--mono);
  font-variant-numeric: tabular-nums;
}

.values th,
.values td {
  padding: 6px 10px;
  border-bottom: 1px solid rgb(51 65 85 / 0.6);
  text-align: right;
  white-space: nowrap;
}

.values tr:last-child > * {
  border-bottom: 0;
}

.values thead th {
  background: var(--surface-2);
  color: var(--text);
  font-weight: 600;
}

.values thead .fn-dot {
  width: 8px;
  height: 8px;
  margin-right: 6px;
  vertical-align: 1px;
  box-shadow: none;
}

.values tbody th {
  color: var(--muted);
  font-weight: 500;
}

.values tbody tr:nth-child(even) {
  background: rgb(15 23 42 / 0.35);
}

/* ---------- syntax help ---------- */

.syntax {
  display: grid;
  gap: 2px;
  margin: 10px 0 0;
  font-size: 0.875rem;
}

.syntax dt {
  margin-top: 6px;
  font-weight: 600;
}

.syntax dd {
  margin: 0;
  color: var(--muted);
  font: 0.8125rem/1.5 var(--mono);
  overflow-wrap: anywhere;
}

/* ---------- toast ---------- */

.toast {
  position: fixed;
  left: 50%;
  bottom: 20px;
  z-index: 10;
  display: flex;
  align-items: center;
  gap: 8px;
  width: max-content;
  max-width: calc(100vw - 32px);
  min-height: 48px;
  padding: 4px 16px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius);
  background: var(--surface-2);
  box-shadow: var(--shadow);
  font-size: 0.875rem;
  opacity: 0;
  visibility: hidden;
  transform: translate(-50%, 12px);
  transition: opacity var(--slow), transform var(--slow), visibility 0s linear 250ms;
}

.toast.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translate(-50%, 0);
  transition-delay: 0s;
}

.toast-action {
  min-height: 40px;
  margin-right: -10px;
  padding: 0 10px;
  border: 0;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--accent);
  font-weight: 700;
  cursor: pointer;
}

.toast-action:hover {
  background: var(--accent-soft);
}

/* ---------- small screens ---------- */

@media (max-width: 639px) {
  .app-header {
    padding: 8px 12px;
  }

  .brand {
    gap: 8px;
    font-size: 1rem;
  }

  .brand-mark {
    width: 26px;
    height: 26px;
  }

  .header-actions {
    gap: 6px;
  }

  .header-actions .btn:not(.btn-lang) {
    padding: 0;
  }

  .btn-label {
    position: absolute;
    width: 1px;
    height: 1px;
    margin: -1px;
    overflow: hidden;
    clip: rect(0 0 0 0);
    white-space: nowrap;
  }
}

@media (max-width: 379px) {
  .brand-mark {
    display: none;
  }
}

/* Desktop with a mouse: denser sliders and toggles (touch screens keep 40 px targets). */
@media (min-width: 900px) and (pointer: fine) {
  input[type="range"] {
    height: 34px;
  }

  .chip {
    min-height: 36px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    transition-duration: 0.01ms !important;
    transition-delay: 0s !important;
    animation-duration: 0.01ms !important;
  }
}