:root {
  color-scheme: light dark;

  --text: #0f172a;
  --muted: #475569;
  --subtle: rgba(71, 85, 105, 0.92);
  --heading: rgba(15, 23, 42, 0.72);
  --accent: #4f46e5;
  --accent-2: #2563eb;
  --danger: #dc2626;
  --border: rgba(15, 23, 42, 0.12);

  --bg-gradient: linear-gradient(120deg, #eef2ff, #f0f9ff, #f8fafc);
  --aurora-vignette:
    radial-gradient(900px 600px at 50% 15%, rgba(255, 255, 255, 0.72), rgba(255, 255, 255, 0) 62%),
    radial-gradient(1200px 900px at 50% 100%, rgba(15, 23, 42, 0.08), transparent 60%),
    radial-gradient(1200px 900px at 0% 60%, rgba(15, 23, 42, 0.06), transparent 60%),
    radial-gradient(1200px 900px at 100% 60%, rgba(15, 23, 42, 0.06), transparent 60%);

  --surface-header: rgba(255, 255, 255, 0.72);
  --surface-page: rgba(255, 255, 255, 0.9);
  --surface-card: rgba(255, 255, 255, 0.78);
  --surface-muted: rgba(255, 255, 255, 0.52);
  --surface-inset: rgba(255, 255, 255, 0.55);
  --surface-choice: rgba(255, 255, 255, 0.65);
  --surface-item: rgba(255, 255, 255, 0.6);
  --surface-btn: rgba(255, 255, 255, 0.72);
  --surface-btn-ghost: rgba(255, 255, 255, 0.62);
  --surface-control: rgba(241, 245, 249, 0.95);
  --surface-control-hover: rgba(226, 232, 240, 0.95);
  --surface-solid: #ffffff;

  /* Back-compat: older rules (kept for readability). */
  --surface: var(--surface-card);
  --surface-strong: var(--surface-page);

  --shadow: 0 18px 60px rgba(15, 23, 42, 0.12);
  --shadow-soft: 0 10px 30px rgba(15, 23, 42, 0.1);
  --focus: rgba(99, 102, 241, 0.6);

  --max: 980px;
  --radius: 16px;

  /* Cursor parallax (set by JS). */
  --mouse-x: 0px;
  --mouse-y: 0px;
  --mouse-gx: 0px;
  --mouse-gy: 0px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --text: #e2e8f0;
    --muted: #94a3b8;
    --subtle: rgba(148, 163, 184, 0.92);
    --heading: rgba(226, 232, 240, 0.92);
    --border: rgba(226, 232, 240, 0.16);

    --bg-gradient: linear-gradient(120deg, #050816, #071a2a, #020617);
    --aurora-vignette:
      radial-gradient(900px 600px at 50% 15%, rgba(2, 6, 23, 0.45), rgba(2, 6, 23, 0) 62%),
      radial-gradient(1200px 900px at 50% 100%, rgba(2, 6, 23, 0.85), transparent 62%),
      radial-gradient(1200px 900px at 0% 60%, rgba(2, 6, 23, 0.6), transparent 62%),
      radial-gradient(1200px 900px at 100% 60%, rgba(2, 6, 23, 0.6), transparent 62%);

    --surface-header: rgba(2, 6, 23, 0.62);
    --surface-page: rgba(2, 6, 23, 0.78);
    --surface-card: rgba(2, 6, 23, 0.62);
    --surface-muted: rgba(2, 6, 23, 0.5);
    --surface-inset: rgba(2, 6, 23, 0.55);
    --surface-choice: rgba(2, 6, 23, 0.62);
    --surface-item: rgba(2, 6, 23, 0.58);
    --surface-btn: rgba(2, 6, 23, 0.58);
    --surface-btn-ghost: rgba(2, 6, 23, 0.48);
    --surface-control: rgba(15, 23, 42, 0.92);
    --surface-control-hover: rgba(30, 41, 59, 0.92);

    --shadow: 0 18px 60px rgba(0, 0, 0, 0.55);
    --shadow-soft: 0 10px 30px rgba(0, 0, 0, 0.4);
    --focus: rgba(129, 140, 248, 0.68);
  }
}

html[data-theme="light"] {
  color-scheme: light;

  --text: #0f172a;
  --muted: #475569;
  --subtle: rgba(71, 85, 105, 0.92);
  --heading: rgba(15, 23, 42, 0.72);
  --border: rgba(15, 23, 42, 0.12);

  --bg-gradient: linear-gradient(120deg, #eef2ff, #f0f9ff, #f8fafc);
  --aurora-vignette:
    radial-gradient(900px 600px at 50% 15%, rgba(255, 255, 255, 0.72), rgba(255, 255, 255, 0) 62%),
    radial-gradient(1200px 900px at 50% 100%, rgba(15, 23, 42, 0.08), transparent 60%),
    radial-gradient(1200px 900px at 0% 60%, rgba(15, 23, 42, 0.06), transparent 60%),
    radial-gradient(1200px 900px at 100% 60%, rgba(15, 23, 42, 0.06), transparent 60%);

  --surface-header: rgba(255, 255, 255, 0.72);
  --surface-page: rgba(255, 255, 255, 0.9);
  --surface-card: rgba(255, 255, 255, 0.78);
  --surface-muted: rgba(255, 255, 255, 0.52);
  --surface-inset: rgba(255, 255, 255, 0.55);
  --surface-choice: rgba(255, 255, 255, 0.65);
  --surface-item: rgba(255, 255, 255, 0.6);
  --surface-btn: rgba(255, 255, 255, 0.72);
  --surface-btn-ghost: rgba(255, 255, 255, 0.62);
  --surface-control: rgba(241, 245, 249, 0.95);
  --surface-control-hover: rgba(226, 232, 240, 0.95);

  --shadow: 0 18px 60px rgba(15, 23, 42, 0.12);
  --shadow-soft: 0 10px 30px rgba(15, 23, 42, 0.1);
  --focus: rgba(99, 102, 241, 0.6);
}

html[data-theme="dark"] {
  color-scheme: dark;

  --text: #e2e8f0;
  --muted: #94a3b8;
  --subtle: rgba(148, 163, 184, 0.92);
  --heading: rgba(226, 232, 240, 0.92);
  --border: rgba(226, 232, 240, 0.16);

  --bg-gradient: linear-gradient(120deg, #050816, #071a2a, #020617);
  --aurora-vignette:
    radial-gradient(900px 600px at 50% 15%, rgba(2, 6, 23, 0.45), rgba(2, 6, 23, 0) 62%),
    radial-gradient(1200px 900px at 50% 100%, rgba(2, 6, 23, 0.85), transparent 62%),
    radial-gradient(1200px 900px at 0% 60%, rgba(2, 6, 23, 0.6), transparent 62%),
    radial-gradient(1200px 900px at 100% 60%, rgba(2, 6, 23, 0.6), transparent 62%);

  --surface-header: rgba(2, 6, 23, 0.62);
  --surface-page: rgba(2, 6, 23, 0.78);
  --surface-card: rgba(2, 6, 23, 0.62);
  --surface-muted: rgba(2, 6, 23, 0.5);
  --surface-inset: rgba(2, 6, 23, 0.55);
  --surface-choice: rgba(2, 6, 23, 0.62);
  --surface-item: rgba(2, 6, 23, 0.58);
  --surface-btn: rgba(2, 6, 23, 0.58);
  --surface-btn-ghost: rgba(2, 6, 23, 0.48);
  --surface-control: rgba(15, 23, 42, 0.92);
  --surface-control-hover: rgba(30, 41, 59, 0.92);

  --shadow: 0 18px 60px rgba(0, 0, 0, 0.55);
  --shadow-soft: 0 10px 30px rgba(0, 0, 0, 0.4);
  --focus: rgba(129, 140, 248, 0.68);
}

* {
  box-sizing: border-box;
}

html,
body {
  height: 100%;
  min-height: 100%;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  line-height: 1.5;
  color: var(--text);
  background: var(--bg-gradient);
  isolation: isolate;
  overflow-x: hidden;
}

/* ---------------------------
 * Aurora / mesh background (subtle + interactive)
 * ------------------------- */

.aurora {
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  overflow: hidden;
}

/* Ensure app UI stays above the background layer. */
body > header,
body > main,
body > footer {
  position: relative;
  z-index: 1;
}

.aurora__base {
  position: absolute;
  inset: -35%;
  background: var(--bg-gradient);
  /*background: linear-gradient(120deg, #eef2ff, #f0f9ff, #f8fafc);*/
  background-size: 260% 260%;
  animation: auroraBaseShift 42s ease-in-out infinite alternate;
  transform: translate3d(var(--mouse-gx), var(--mouse-gy), 0) scale(1.08);
  filter: saturate(1.12);
  will-change: transform;
}

@keyframes auroraBaseShift {
  0% {
    background-position: 12% 18%;
  }
  50% {
    background-position: 88% 22%;
  }
  100% {
    background-position: 18% 86%;
  }
}

.aurora__blobs {
  position: absolute;
  inset: -20%;
  transform: translate3d(var(--mouse-x), var(--mouse-y), 0);
  will-change: transform;
}

.aurora__blob {
  position: absolute;
  border-radius: 999px;
  opacity: var(--blob-opacity, 0.24);
  filter: blur(var(--blob-blur, 110px));
  background: radial-gradient(circle at 30% 30%, var(--blob-color, rgba(99, 102, 241, 0.25)), transparent 62%);
  transform: translate3d(0, 0, 0);
  will-change: transform;
}

.aurora__blob--1 {
  left: 8%;
  top: 10%;
  width: 520px;
  height: 420px;
  --blob-color: rgba(99, 102, 241, 0.25);
  --blob-blur: 120px;
  /*--blob-blur: 120px;*/
  --blob-opacity: 0.3;
  animation: auroraBlob1 18s ease-in-out infinite alternate;
}

.aurora__blob--2 {
  left: 62%;
  top: 6%;
  width: 560px;
  height: 460px;
  --blob-color: rgba(56, 189, 248, 0.22);
  --blob-blur: 130px;
  --blob-opacity: 0.26;
  animation: auroraBlob2 20s ease-in-out infinite alternate;
}

.aurora__blob--3 {
  left: 52%;
  top: 58%;
  width: 640px;
  height: 520px;
  --blob-color: rgba(168, 85, 247, 0.2);
  --blob-blur: 140px;
  --blob-opacity: 0.24;
  animation: auroraBlob3 22s ease-in-out infinite alternate;
}

.aurora__blob--4 {
  left: 16%;
  top: 62%;
  width: 520px;
  height: 520px;
  --blob-color: rgba(14, 165, 233, 0.16);
  --blob-blur: 120px;
  --blob-opacity: 0.22;
  animation: auroraBlob4 24s ease-in-out infinite alternate;
}

@keyframes auroraBlob1 {
  0% {
    transform: translate3d(-70px, -34px, 0) scale(1);
  }
  100% {
    transform: translate3d(76px, 48px, 0) scale(1.07);
  }
}

@keyframes auroraBlob2 {
  0% {
    transform: translate3d(56px, -44px, 0) scale(1);
  }
  100% {
    transform: translate3d(-66px, 46px, 0) scale(1.08);
  }
}

@keyframes auroraBlob3 {
  0% {
    transform: translate3d(40px, 48px, 0) scale(1.03);
  }
  100% {
    transform: translate3d(-52px, -58px, 0) scale(1.1);
  }
}

@keyframes auroraBlob4 {
  0% {
    transform: translate3d(-46px, 42px, 0) scale(1.02);
  }
  100% {
    transform: translate3d(54px, -52px, 0) scale(1.09);
  }
}

.aurora__vignette {
  position: absolute;
  inset: 0;
  background: var(--aurora-vignette);
}

/* Touch devices / no mouse: disable cursor tracking (keep slow CSS blob animation). */
html.bg-no-pointer .aurora__blobs {
  transform: translate3d(0, 0, 0);
}

/* Reduced motion: freeze background animations. */
html.bg-reduce-motion .aurora__base,
html.bg-reduce-motion .aurora__blob {
  animation: none !important;
}

@media (prefers-reduced-motion: reduce) {
  .aurora__base,
  .aurora__blob {
    animation: none !important;
  }
}

/* ---------------------------
 * Typography + links
 * ------------------------- */

a {
  color: inherit;
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

h1 {
  margin: 0 0 0.6rem;
  letter-spacing: 0.2px;
}

h2 {
  margin: 0 0 0.75rem;
  font-size: 1.15rem;
  color: var(--heading);
}

.muted {
  color: var(--muted);
}

/* ---------------------------
 * Layout / containers
 * ------------------------- */

.container {
  width: min(100% - 2rem, var(--max));
  margin-inline: auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: var(--surface-header);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.75rem 0;
  gap: 1rem;
}

.brand {
  font-weight: 700;
  letter-spacing: 0.2px;
}

.top-nav {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.header-actions {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.theme-toggle {
  white-space: nowrap;
  flex: 0 0 auto;
}

.nav-link {
  padding: 0.35rem 0.6rem;
  border-radius: 0.6rem;
}

.nav-link.is-active {
  background: rgba(99, 102, 241, 0.12);
  outline: 1px solid rgba(99, 102, 241, 0.22);
}

/* ---------------------------
 * Top nav dropdowns
 * ------------------------- */

.nav-dropdown {
  position: relative;
  display: inline-flex;
  align-items: center;
}

.nav-dropdown__toggle {
  border: 0;
  background: transparent;
  font: inherit;
  color: inherit;
  cursor: pointer;
}

.nav-dropdown__menu {
  position: absolute;
  top: 100%;
  left: 0;
  min-width: 15rem;
  padding: 0.35rem;
  margin-top: 0;
  border: 1px solid var(--border);
  border-radius: 0.85rem;
  background: var(--surface-page);
  box-shadow: var(--shadow-soft);
  display: none;
}

.nav-dropdown:hover .nav-dropdown__menu,
.nav-dropdown:focus-within .nav-dropdown__menu {
  display: block;
}

.nav-dropdown__item {
  display: block;
  white-space: nowrap;
}

main {
  padding: 1.25rem 0 2rem;
}

/* Readability: main content sits on a frosted “card”. */
main.container {
  padding: 1.25rem 1rem 1.75rem;
  margin-top: 1rem;
  margin-bottom: 1.25rem;
  border: 1px solid var(--border);
  border-radius: calc(var(--radius) + 4px);
  background: var(--surface-page);
  box-shadow: var(--shadow-soft);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

@media (min-width: 640px) {
  main.container {
    padding: 1.5rem 1.5rem 2rem;
  }
}

.page-title {
  margin: 0 0 0.35rem;
  font-size: 1.85rem;
  letter-spacing: 0.2px;
}

.page-lead {
  margin: 0 0 1rem;
  color: var(--muted);
}

.card {
  padding: 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface-card);
  box-shadow: var(--shadow-soft);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
}

.card__header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-bottom: 0.6rem;
}

.site-footer {
  border-top: 1px solid var(--border);
  padding: 1rem 0;
  color: var(--muted);
}

.list {
  margin: 0;
  padding-left: 1.2rem;
  color: var(--text);
}

/* ---------------------------
 * Grid (mobile-first)
 * ------------------------- */

.calc-grid {
  display: grid;
  gap: 1rem;
}

.calc-grid__main {
  display: grid;
  gap: 1rem;
}

@media (min-width: 960px) {
  .calc-grid {
    grid-template-columns: minmax(0, 720px) minmax(0, 1fr);
    align-items: start;
    justify-content: center;
  }

  .card--history {
    position: sticky;
    top: 5rem;
    align-self: start;
  }
}

/* ---------------------------
 * Controls + focus
 * ------------------------- */

.control {
  width: 100%;
  border-radius: 0.8rem;
  border: 1px solid var(--border);
  background: var(--surface-control);
  color: var(--text);
  padding: 0.65rem 0.75rem;
  font: inherit;
  transition: border-color 120ms ease, box-shadow 120ms ease, background 120ms ease;
}

.control:hover {
  border-color: rgba(99, 102, 241, 0.28);
  background: var(--surface-control-hover);
}

.control:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
  box-shadow: 0 0 0 6px rgba(99, 102, 241, 0.12);
}

.control[aria-invalid="true"] {
  border-color: rgba(220, 38, 38, 0.5);
  box-shadow: 0 0 0 1px rgba(220, 38, 38, 0.22) inset;
}

.btn {
  border: 1px solid var(--border);
  border-radius: 0.85rem;
  padding: 0.7rem 0.95rem;
  background: var(--surface-btn);
  color: var(--text);
  cursor: pointer;
  font: inherit;
  transition: transform 90ms ease, border-color 120ms ease, background 120ms ease, opacity 120ms ease;
}

.btn:hover {
  border-color: rgba(99, 102, 241, 0.25);
}

.btn:active {
  transform: translateY(1px);
}

.btn:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
  box-shadow: 0 0 0 6px rgba(99, 102, 241, 0.12);
}

.btn[disabled] {
  opacity: 0.55;
  cursor: not-allowed;
  transform: none;
}

.btn--primary {
  border-color: rgba(99, 102, 241, 0.35);
  background: rgba(99, 102, 241, 0.14);
}

.btn--ghost {
  background: var(--surface-btn-ghost);
}

.btn--small {
  padding: 0.45rem 0.7rem;
  border-radius: 0.75rem;
}

/* ---------------------------
 * Form fields
 * ------------------------- */

.fieldset {
  border: 1px solid var(--border);
  border-radius: 0.85rem;
  padding: 0.85rem;
  margin: 0 0 1rem;
  background: var(--surface-muted);
}

.fieldset__legend {
  padding: 0 0.5rem;
  color: var(--muted);
}

.field-grid {
  display: grid;
  gap: 0.9rem;
  margin-bottom: 0.9rem;
}

@media (min-width: 640px) {
  .field-grid {
    grid-template-columns: 1fr 1fr;
  }
}

.field-grid--single {
  grid-template-columns: 1fr;
}

.field__label {
  display: block;
  margin-bottom: 0.35rem;
  color: var(--muted);
}

.field__help {
  margin: 0.35rem 0 0;
  font-size: 0.9rem;
  color: var(--subtle);
}

.field__error {
  margin: 0.25rem 0 0;
  font-size: 0.92rem;
  color: var(--danger);
  min-height: 1.25em;
}

.actions {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
  justify-content: flex-end;
}

/* ---------------------------
 * Sentence-style percent inputs
 * ------------------------- */

.sentence-row {
  margin-bottom: 0.9rem;
}

.sentence {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 0.55rem;
  padding: 0.85rem;
  border: 1px solid var(--border);
  border-radius: 0.85rem;
  background: var(--surface-inset);
}

.sentence__slot {
  display: inline-flex;
  align-items: baseline;
  flex: 0 1 auto;
}

.control--inline {
  width: clamp(6.5rem, 16vw, 9.5rem);
  max-width: 100%;
  padding: 0.6rem 0.7rem;
}

.sentence__meta {
  display: grid;
  gap: 0.85rem;
  margin-top: 0.6rem;
}

@media (min-width: 640px) {
  .sentence__meta {
    grid-template-columns: 1fr 1fr;
  }
}

/* ---------------------------
 * Mode tabs (radios)
 * ------------------------- */

.mode-tabs {
  display: grid;
  gap: 0.6rem;
}

@media (min-width: 720px) {
  .mode-tabs {
    grid-template-columns: 1fr 1fr;
  }
}

.mode-tabs__item {
  position: relative;
}

.mode-tabs__radio {
  position: absolute;
  inset: 0;
  opacity: 0;
}

.mode-tabs__label {
  display: block;
  padding: 0.7rem 0.8rem;
  border-radius: 0.85rem;
  border: 1px solid var(--border);
  background: var(--surface-choice);
  cursor: pointer;
  user-select: none;
}

.mode-tabs__title {
  display: block;
  font-weight: 650;
}

.mode-tabs__desc {
  display: block;
  margin-top: 0.15rem;
  font-size: 0.9rem;
  color: var(--muted);
}

.mode-tabs__radio:checked + .mode-tabs__label {
  border-color: rgba(99, 102, 241, 0.45);
  background: rgba(99, 102, 241, 0.12);
}

.mode-tabs__radio:focus-visible + .mode-tabs__label {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
  box-shadow: 0 0 0 6px rgba(99, 102, 241, 0.12);
}

/* ---------------------------
 * Result + history
 * ------------------------- */

.result__value {
  font-size: 1.45rem;
  font-weight: 750;
  letter-spacing: 0.2px;
}

.result__explain {
  margin-top: 0.3rem;
  color: var(--muted);
}

.result__steps {
  margin: 0.6rem 0 0;
  padding-left: 1.25rem;
  color: var(--subtle);
}

.result__steps > li + li {
  margin-top: 0.25rem;
}

.history__list {
  margin: 0.6rem 0 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 0.6rem;
}

.history__item {
  border: 1px solid var(--border);
  border-radius: 0.8rem;
  background: var(--surface-item);
  padding: 0.65rem 0.75rem;
}

.history__ts {
  display: block;
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 0.86rem;
  color: var(--subtle);
}

.history__expr {
  display: block;
  margin-top: 0.15rem;
}

.history__res {
  display: block;
  margin-top: 0.15rem;
  color: var(--muted);
}

/* Utility: only for screen readers */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* ---------------------------
 * Language switcher
 * ------------------------- */

.lang-switcher {
  display: inline-flex;
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  overflow: hidden;
  flex: 0 0 auto;
}

.lang-btn {
  border: 0;
  background: transparent;
  color: var(--muted);
  font: inherit;
  font-size: 0.78rem;
  font-weight: 600;
  padding: 0.25rem 0.5rem;
  cursor: pointer;
  transition: background 120ms ease, color 120ms ease;
  line-height: 1.4;
}

.lang-btn:hover {
  color: var(--text);
}

.lang-btn[aria-pressed="true"] {
  background: var(--accent);
  color: #fff;
}

.lang-btn[aria-pressed="true"]:hover {
  color: #fff;
}

.lang-btn:not(:last-child) {
  border-right: 1px solid var(--border);
}