:root {
  --bg: #f4f7fb;
  --surface: #ffffff;
  --surface-soft: #f8fafc;
  --text: #172033;
  --muted: #637083;
  --border: #dbe3ee;
  --primary: #4658d9;
  --primary-dark: #3443b5;
  --primary-soft: #eef0ff;
  --accent: #0f9f91;
  --accent-soft: #e8faf7;
  --danger: #c33c54;
  --danger-soft: #fff0f3;
  --shadow: 0 14px 35px rgba(33, 48, 84, 0.09);
  --radius: 18px;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

[data-theme="dark"] {
  --bg: #0e1422;
  --surface: #171f31;
  --surface-soft: #111a2a;
  --text: #edf2ff;
  --muted: #a7b0c2;
  --border: #2d3950;
  --primary: #8390ff;
  --primary-dark: #9aa4ff;
  --primary-soft: #242d55;
  --accent: #4dd4c4;
  --accent-soft: #163b3c;
  --danger: #ff8197;
  --danger-soft: #4a2430;
  --shadow: 0 18px 45px rgba(0, 0, 0, 0.28);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.6;
  transition: background-color 0.2s ease, color 0.2s ease;
}

button,
input,
select {
  font: inherit;
}

button {
  cursor: pointer;
}

.container {
  width: min(1160px, calc(100% - 32px));
  margin-inline: auto;
}

.hero {
  position: relative;
  overflow: hidden;
  padding: 64px 0 78px;
  color: white;
  background:
    radial-gradient(circle at 88% 18%, rgba(72, 214, 199, 0.28), transparent 30%),
    linear-gradient(135deg, #27358f 0%, #4658d9 52%, #287c9b 100%);
}

.hero::after {
  content: "";
  position: absolute;
  right: -120px;
  bottom: -180px;
  width: 420px;
  height: 420px;
  border: 1px solid rgba(255,255,255,0.14);
  border-radius: 50%;
  box-shadow: 0 0 0 52px rgba(255,255,255,0.04), 0 0 0 104px rgba(255,255,255,0.025);
}

.hero__inner {
  position: relative;
  z-index: 1;
  display: flex;
  justify-content: space-between;
  align-items: flex-end;
  gap: 40px;
}

.eyebrow,
.section-kicker {
  margin: 0 0 8px;
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.eyebrow {
  color: #cdd6ff;
}

.hero h1 {
  margin: 0;
  max-width: 760px;
  font-size: clamp(2.3rem, 6vw, 4.4rem);
  line-height: 1.05;
  letter-spacing: -0.045em;
}

.hero__subtitle {
  max-width: 760px;
  margin: 18px 0 0;
  color: rgba(255,255,255,0.86);
  font-size: 1.05rem;
}

.hero__badge {
  display: grid;
  grid-template-columns: repeat(2, max-content);
  gap: 8px;
  flex-shrink: 0;
}

.hero__badge span {
  padding: 8px 12px;
  border: 1px solid rgba(255,255,255,0.25);
  border-radius: 999px;
  background: rgba(255,255,255,0.1);
  backdrop-filter: blur(8px);
  font-size: 0.82rem;
  font-weight: 700;
}

.main-layout {
  display: grid;
  gap: 24px;
  margin-top: -36px;
  padding-bottom: 56px;
  position: relative;
  z-index: 2;
}

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

.input-card,
.result-card,
.reference-card,
.steps-toolbar {
  padding: clamp(20px, 4vw, 32px);
}

.section-heading {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  margin-bottom: 24px;
}

.section-heading h2,
.steps-toolbar h2 {
  margin: 0;
  font-size: clamp(1.35rem, 3vw, 1.85rem);
  letter-spacing: -0.025em;
}

.section-kicker {
  color: var(--primary);
}

.icon-button {
  width: 42px;
  height: 42px;
  border: 1px solid var(--border);
  border-radius: 12px;
  color: var(--text);
  background: var(--surface-soft);
}

.mode-selector {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 0 0 24px;
  padding: 0;
  border: 0;
}

.mode-selector legend {
  width: 100%;
  margin-bottom: 9px;
  font-weight: 700;
}

.mode-option {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface-soft);
  transition: 0.18s ease;
}

.mode-option:has(input:checked) {
  border-color: var(--primary);
  background: var(--primary-soft);
  box-shadow: inset 0 0 0 1px var(--primary);
}

.mode-option input {
  width: 18px;
  height: 18px;
  accent-color: var(--primary);
}

.mode-option span {
  display: grid;
}

.mode-option small {
  color: var(--muted);
}

.form-group {
  margin-bottom: 20px;
}

.label-row {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 8px;
}

label,
legend {
  font-weight: 700;
}

.char-count {
  color: var(--muted);
  font-family: var(--mono);
  font-size: 0.82rem;
}

input[type="text"] {
  width: 100%;
  padding: 14px 15px;
  border: 1px solid var(--border);
  border-radius: 12px;
  outline: none;
  color: var(--text);
  background: var(--surface-soft);
  font-family: var(--mono);
  letter-spacing: 0.06em;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

input[type="text"]:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 4px color-mix(in srgb, var(--primary) 16%, transparent);
}

input.invalid {
  border-color: var(--danger);
  background: var(--danger-soft);
}

.form-group small {
  display: block;
  margin-top: 7px;
  color: var(--muted);
}

.error-message {
  min-height: 1.4em;
  margin: 4px 0 0;
  color: var(--danger);
  font-size: 0.88rem;
  font-weight: 650;
}

.form-actions,
.toolbar-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.example-panel {
  margin: 2px 0 24px;
  padding: 18px;
  border: 1px solid color-mix(in srgb, var(--primary) 30%, var(--border));
  border-radius: 16px;
  background: linear-gradient(145deg, var(--primary-soft), var(--surface-soft));
}

.example-panel__header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 14px;
}

.example-panel__header > div {
  display: grid;
  gap: 2px;
}

.example-panel__eyebrow {
  color: var(--primary);
  font-size: 0.75rem;
  font-weight: 850;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.example-chip {
  flex-shrink: 0;
  padding: 5px 9px;
  border: 1px solid color-mix(in srgb, var(--primary) 35%, transparent);
  border-radius: 999px;
  color: var(--primary);
  background: var(--surface);
  font-family: var(--mono);
  font-size: 0.75rem;
  font-weight: 800;
}

.example-control-row {
  display: grid;
  grid-template-columns: minmax(220px, 1fr) auto auto;
  gap: 10px;
  margin-top: 8px;
}

select {
  width: 100%;
  min-height: 44px;
  padding: 10px 38px 10px 13px;
  border: 1px solid var(--border);
  border-radius: 12px;
  outline: none;
  color: var(--text);
  background: var(--surface);
  font-weight: 650;
}

select:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 4px color-mix(in srgb, var(--primary) 16%, transparent);
}

.button--example {
  color: white;
  background: var(--accent);
}

.button--example:hover {
  filter: brightness(0.93);
}

.example-preview {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 9px;
  margin-top: 13px;
}

.example-preview__item {
  min-width: 0;
  padding: 11px 12px;
  border: 1px solid var(--border);
  border-radius: 11px;
  background: color-mix(in srgb, var(--surface) 88%, transparent);
}

.example-preview__item span,
.example-preview__item small {
  display: block;
  color: var(--muted);
  font-size: 0.75rem;
}

.example-preview__item strong {
  display: block;
  margin: 3px 0 1px;
  overflow-wrap: anywhere;
  font-size: 0.78rem;
}

.example-preview__active {
  border-color: color-mix(in srgb, var(--accent) 45%, var(--border));
  box-shadow: inset 3px 0 0 var(--accent);
}

.example-panel > small {
  display: block;
  margin-top: 10px;
  color: var(--muted);
}

.copy-button {
  border: 0;
  color: var(--primary);
  background: transparent;
  font-weight: 750;
}

.button {
  min-height: 44px;
  padding: 10px 18px;
  border: 1px solid transparent;
  border-radius: 12px;
  font-weight: 800;
  letter-spacing: 0.02em;
  transition: transform 0.15s ease, background-color 0.15s ease;
}

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

.button--primary {
  color: white;
  background: var(--primary);
}

.button--primary:hover {
  background: var(--primary-dark);
}

.button--secondary {
  border-color: var(--border);
  color: var(--text);
  background: var(--surface-soft);
}

.button--small {
  min-height: 38px;
  padding: 7px 12px;
  font-size: 0.88rem;
}

.result-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr;
  gap: 14px;
}

.result-box {
  position: relative;
  display: grid;
  gap: 7px;
  min-width: 0;
  padding: 18px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface-soft);
}

.result-box > span {
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 650;
}

.result-value {
  overflow-wrap: anywhere;
  font-size: clamp(1.12rem, 4vw, 1.55rem);
}

.copy-button {
  position: absolute;
  top: 13px;
  right: 13px;
  padding: 4px 8px;
  font-size: 0.8rem;
}

.result-summary {
  margin-top: 16px;
  padding: 14px 16px;
  border-left: 4px solid var(--accent);
  border-radius: 0 12px 12px 0;
  background: var(--accent-soft);
}

.status-badge {
  padding: 7px 12px;
  border-radius: 999px;
  color: var(--primary);
  background: var(--primary-soft);
  font-size: 0.84rem;
  font-weight: 800;
}

.steps-panel {
  display: grid;
  gap: 16px;
}

.steps-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 20px;
}

#stepsContainer {
  display: grid;
  gap: 14px;
}

details.step-card {
  overflow: clip;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

details.step-card[open] {
  border-color: color-mix(in srgb, var(--primary) 42%, var(--border));
}

.step-card summary {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 18px 22px;
  cursor: pointer;
  list-style: none;
  font-weight: 800;
}

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

.step-card summary::after {
  content: "+";
  margin-left: auto;
  color: var(--primary);
  font-size: 1.45rem;
  line-height: 1;
}

.step-card[open] summary::after {
  content: "−";
}

.step-number {
  display: grid;
  place-items: center;
  width: 32px;
  height: 32px;
  flex: 0 0 auto;
  border-radius: 10px;
  color: white;
  background: var(--primary);
  font-size: 0.88rem;
}

.step-content {
  padding: 0 22px 24px;
  border-top: 1px solid var(--border);
}

.step-description {
  margin: 18px 0;
  color: var(--muted);
}

.subsection {
  margin-top: 20px;
}

.subsection h4 {
  margin: 0 0 10px;
}

.operation-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  align-items: center;
}

.operation-grid.two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.operation-arrow {
  display: grid;
  place-items: center;
  color: var(--primary);
  font-size: 1.4rem;
  font-weight: 900;
}

.matrix-panel {
  min-width: 0;
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface-soft);
}

.matrix-panel > span {
  display: block;
  margin-bottom: 9px;
  color: var(--muted);
  font-size: 0.84rem;
  font-weight: 700;
}

.state-matrix {
  display: grid;
  grid-template-columns: repeat(2, minmax(55px, 1fr));
  gap: 7px;
  max-width: 260px;
}

.nibble-cell {
  display: grid;
  place-items: center;
  min-height: 52px;
  padding: 7px;
  border: 1px solid color-mix(in srgb, var(--primary) 35%, var(--border));
  border-radius: 10px;
  color: var(--text);
  background: var(--primary-soft);
  font-family: var(--mono);
  font-size: 1rem;
  font-weight: 850;
}

.nibble-cell small {
  color: var(--muted);
  font-size: 0.66rem;
  font-weight: 600;
}

.word-table,
.reference-table,
.comparison-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9rem;
}

.word-table th,
.word-table td,
.reference-table th,
.reference-table td,
.comparison-table th,
.comparison-table td {
  padding: 9px 10px;
  border: 1px solid var(--border);
  text-align: center;
}

.word-table th,
.reference-table th,
.comparison-table th {
  background: var(--primary-soft);
  color: var(--text);
}

.table-scroll {
  overflow-x: auto;
}

.code-line,
.formula-box,
.gf-detail {
  overflow-x: auto;
  padding: 12px 14px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--surface-soft);
}

.code-line,
.formula-box {
  font-family: var(--mono);
}

.formula-box {
  margin: 10px 0;
}

.nibble-transform-list,
.gf-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.nibble-transform,
.gf-detail {
  min-width: 0;
}

.nibble-transform {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  padding: 11px 13px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--surface-soft);
  font-family: var(--mono);
}

.gf-detail summary {
  cursor: pointer;
  color: var(--primary);
  font-weight: 800;
}

.gf-detail pre {
  margin: 10px 0 0;
  white-space: pre-wrap;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 0.78rem;
  line-height: 1.55;
}

.reference-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 22px;
}

.reference-grid h3,
.constant-card h3 {
  margin: 0 0 10px;
  font-size: 1rem;
}

.constant-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 12px;
  margin-top: 24px;
}

.constant-card {
  padding: 16px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface-soft);
}

.constant-card p {
  margin: 5px 0;
}

.math-matrix {
  display: grid;
  grid-template-columns: repeat(2, 42px);
  gap: 6px;
  width: max-content;
  padding: 0 10px;
  border-left: 2px solid var(--text);
  border-right: 2px solid var(--text);
  font-family: var(--mono);
}

.math-matrix span {
  text-align: center;
}

.formula {
  font-family: Georgia, serif;
  font-style: italic;
}

.mono {
  font-family: var(--mono);
}

.hidden {
  display: none !important;
}

.toast {
  position: fixed;
  left: 50%;
  bottom: 24px;
  z-index: 20;
  transform: translate(-50%, 18px);
  padding: 10px 14px;
  border-radius: 10px;
  color: white;
  background: #20283a;
  box-shadow: var(--shadow);
  opacity: 0;
  pointer-events: none;
  transition: 0.2s ease;
}

.toast.show {
  transform: translate(-50%, 0);
  opacity: 1;
}

footer {
  border-top: 1px solid var(--border);
  background: var(--surface);
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  padding-block: 26px;
  color: var(--muted);
  font-size: 0.85rem;
}

.footer-inner p {
  margin: 0;
}

@media (max-width: 850px) {
  .hero__inner,
  .steps-toolbar,
  .footer-inner {
    align-items: flex-start;
    flex-direction: column;
  }

  .hero__badge {
    grid-template-columns: repeat(4, max-content);
  }

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

  .operation-grid {
    grid-template-columns: 1fr;
  }

  .operation-arrow {
    transform: rotate(90deg);
  }
}

@media (max-width: 640px) {
  .hero {
    padding: 48px 0 66px;
  }

  .hero__badge,
  .mode-selector,
  .result-grid,
  .reference-grid,
  .constant-grid,
  .nibble-transform-list,
  .gf-grid,
  .operation-grid.two {
    grid-template-columns: 1fr;
  }

  .hero__badge {
    width: 100%;
  }

  .hero__badge span {
    text-align: center;
  }

  .section-heading {
    align-items: flex-start;
  }

  .toolbar-actions {
    width: 100%;
  }

  .toolbar-actions .button {
    flex: 1;
  }

  .step-card summary {
    padding: 16px;
  }

  .step-content {
    padding: 0 16px 20px;
  }

  .state-matrix {
    max-width: none;
  }
}

@media (max-width: 820px) {
  .example-control-row {
    grid-template-columns: 1fr 1fr;
  }

  .example-control-row select {
    grid-column: 1 / -1;
  }

  .example-preview {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 520px) {
  .example-control-row {
    grid-template-columns: 1fr;
  }

  .example-control-row select {
    grid-column: auto;
  }

  .example-control-row .button {
    width: 100%;
  }
}