:root {
  --color-bg: #f8fafc;
  --color-surface: #ffffff;
  --color-surface-elevated: #ffffff;
  --color-border: #e2e8f0;
  --color-border-strong: #cbd5e1;
  --color-text: #0f172a;
  --color-text-muted: #64748b;
  --color-primary: #4f46e5;
  --color-primary-hover: #4338ca;
  --color-primary-light: #eef2ff;
  --color-accent: #06b6d4;
  --color-accent-light: #ecfeff;
  --color-success: #10b981;
  --color-placeholder: #94a3b8;
  --color-output-bg: #eef2ff;
  --color-output-border: #c7d2fe;
  --color-hover-surface: rgba(255, 255, 255, 0.7);
  --color-focus-ring: rgba(79, 70, 229, 0.15);
  --color-card-hover-border: #c7d2fe;
  --gradient-primary: rgba(79, 70, 229, 0.15);
  --gradient-accent: rgba(6, 182, 212, 0.1);
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.05);
  --shadow-md: 0 4px 16px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 12px 40px rgba(79, 70, 229, 0.12);
  --shadow-info: 0 -4px 24px rgba(15, 23, 42, 0.04);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --font-sans: "DM Sans", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, monospace;
}

[data-theme="dark"] {
  --color-bg: #0f172a;
  --color-surface: #1e293b;
  --color-surface-elevated: #273449;
  --color-border: #334155;
  --color-border-strong: #475569;
  --color-text: #f1f5f9;
  --color-text-muted: #94a3b8;
  --color-primary: #818cf8;
  --color-primary-hover: #a5b4fc;
  --color-primary-light: rgba(99, 102, 241, 0.18);
  --color-accent: #22d3ee;
  --color-accent-light: rgba(34, 211, 238, 0.12);
  --color-placeholder: #64748b;
  --color-output-bg: rgba(99, 102, 241, 0.12);
  --color-output-border: #4338ca;
  --color-hover-surface: rgba(255, 255, 255, 0.06);
  --color-focus-ring: rgba(129, 140, 248, 0.25);
  --color-card-hover-border: #4338ca;
  --gradient-primary: rgba(99, 102, 241, 0.2);
  --gradient-accent: rgba(34, 211, 238, 0.08);
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.35);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.45);
  --shadow-info: 0 -4px 24px rgba(0, 0, 0, 0.2);
}

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

*::selection {
  background-color: var(--color-primary-light);
  color: var(--color-primary);
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.65;
  color: var(--color-text);
  background:
    radial-gradient(ellipse 80% 50% at 50% -20%, var(--gradient-primary), transparent),
    radial-gradient(ellipse 60% 40% at 100% 0%, var(--gradient-accent), transparent),
    var(--color-bg);
  min-height: 100vh;
  transition: background-color 0.25s ease, color 0.25s ease;
}

.container {
  width: 100%;
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 1.25rem;
}

a {
  color: var(--color-primary);
  font-weight: 600;
  text-decoration: none;
  transition: color 0.15s ease;
}

a:hover {
  color: var(--color-primary-hover);
}

strong {
  font-weight: 600;
}

/* Header */
.site-header {
  padding: 2.5rem 0 1.5rem;
}

.header-bar {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
}

.header-content {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

.theme-toggle {
  flex-shrink: 0;
  display: grid;
  place-items: center;
  width: 2.75rem;
  height: 2.75rem;
  border: 1.5px solid var(--color-border);
  border-radius: 50%;
  background: var(--color-surface);
  color: var(--color-text-muted);
  cursor: pointer;
  transition: all 0.2s ease;
  box-shadow: var(--shadow-sm);
}

.theme-toggle:hover {
  color: var(--color-primary);
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.theme-toggle svg {
  width: 1.2rem;
  height: 1.2rem;
  grid-area: 1 / 1;
  transition: opacity 0.2s ease, transform 0.2s ease;
}

.theme-toggle .icon-sun {
  opacity: 1;
  transform: rotate(0) scale(1);
}

.theme-toggle .icon-moon {
  opacity: 0;
  transform: rotate(-30deg) scale(0.8);
}

[data-theme="dark"] .theme-toggle .icon-sun {
  opacity: 0;
  transform: rotate(30deg) scale(0.8);
}

[data-theme="dark"] .theme-toggle .icon-moon {
  opacity: 1;
  transform: rotate(0) scale(1);
}

[data-theme="dark"] .theme-toggle {
  color: var(--color-primary);
}

.logo-mark {
  flex-shrink: 0;
  width: 3.5rem;
  height: 3.5rem;
  display: grid;
  place-items: center;
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  border-radius: var(--radius-md);
  color: white;
  box-shadow: var(--shadow-md);
}

.logo-mark svg {
  width: 1.75rem;
  height: 1.75rem;
}

.eyebrow {
  margin: 0 0 0.25rem;
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-primary);
}

h1 {
  margin: 0;
  font-size: clamp(1.5rem, 4vw, 2.1rem);
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
}

h2 {
  margin: 0 0 1rem;
  font-size: 1.6rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

h3 {
  margin: 0 0 0.75rem;
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-primary);
}

/* Hero */
.hero {
  margin-bottom: 1.5rem;
}

.hero-text {
  margin: 0;
  font-size: 1.05rem;
  color: var(--color-text-muted);
  max-width: 72ch;
}

.fieldname {
  font-family: var(--font-mono);
  font-size: 0.9em;
  font-weight: 500;
  color: var(--color-primary);
  background: var(--color-primary-light);
  padding: 0.1em 0.45em;
  border-radius: 4px;
}

/* Calculator */
.calculator-section {
  margin-bottom: 3rem;
  position: relative;
}

.calculator-card,
.info-section,
.info-card,
textarea,
.theme-toggle,
.swap-btn,
.action-btn,
.format-toggle,
.operations {
  transition: background-color 0.25s ease, border-color 0.25s ease, color 0.25s ease, box-shadow 0.25s ease;
}

.calculator-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--shadow-lg);
}

.operations {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 1.5rem;
  padding: 0.35rem;
  background: var(--color-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
}

.op-btn {
  flex: 1;
  min-width: 7rem;
  padding: 0.7rem 1.25rem;
  border: none;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--color-text-muted);
  font-family: inherit;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
}

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

.op-btn.active {
  background: var(--color-primary);
  color: white;
  box-shadow: var(--shadow-sm);
}

.inputs-grid {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 1rem;
  align-items: center;
  margin-bottom: 1.5rem;
}

.input-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.input-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text);
  letter-spacing: 0.01em;
}

.textarea-wrap {
  position: relative;
}

textarea {
  width: 100%;
  padding: 0.9rem 1rem;
  padding-bottom: 2.5rem;
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg);
  font-family: var(--font-mono);
  font-size: 0.875rem;
  line-height: 1.6;
  color: var(--color-text);
  resize: vertical;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

textarea:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-focus-ring);
  background: var(--color-surface);
}

textarea::placeholder {
  color: var(--color-placeholder);
  font-family: var(--font-sans);
}

#output {
  background: var(--color-output-bg);
  border-color: var(--color-output-border);
  cursor: default;
}

.swap-col {
  display: flex;
  justify-content: center;
  padding-top: 1.75rem;
}

.swap-btn {
  display: grid;
  place-items: center;
  width: 2.75rem;
  height: 2.75rem;
  border: 1.5px solid var(--color-border);
  border-radius: 50%;
  background: var(--color-surface);
  color: var(--color-primary);
  cursor: pointer;
  transition: all 0.2s ease;
  box-shadow: var(--shadow-sm);
}

.swap-btn:hover {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: white;
  transform: rotate(180deg);
}

.swap-btn svg {
  width: 1.25rem;
  height: 1.25rem;
}

.action-btn {
  position: absolute;
  right: 0.6rem;
  bottom: 0.6rem;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.35rem 0.65rem;
  border: 1px solid var(--color-border);
  border-radius: 6px;
  background: var(--color-surface);
  color: var(--color-text-muted);
  font-family: inherit;
  font-size: 0.75rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
}

.action-btn:hover {
  color: var(--color-primary);
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.action-btn svg {
  width: 0.9rem;
  height: 0.9rem;
}

.output-section {
  border-top: 1px solid var(--color-border);
  padding-top: 1.5rem;
}

.output-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 0.5rem;
}

.row-count {
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
}

.format-options {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 0.85rem;
}

.format-toggle {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.4rem 0.85rem;
  border: 1.5px solid var(--color-border);
  border-radius: 999px;
  background: var(--color-surface);
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--color-text-muted);
  cursor: pointer;
  transition: all 0.15s ease;
  user-select: none;
}

.format-toggle:has(input:checked) {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
  color: var(--color-primary);
}

.format-toggle input {
  accent-color: var(--color-primary);
  width: 0.95rem;
  height: 0.95rem;
  cursor: pointer;
}

.format-hint {
  margin: 0.75rem 0 0;
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

/* Toast */
.toast {
  position: fixed;
  bottom: 1.5rem;
  left: 50%;
  transform: translateX(-50%) translateY(120%);
  padding: 0.75rem 1.25rem;
  background: var(--color-text);
  color: white;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 500;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  transition: all 0.3s ease;
  z-index: 100;
  pointer-events: none;
}

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

.toast.success {
  background: var(--color-success);
}

.toast.error {
  background: #ef4444;
}

/* Info section */
.info-section {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: 3rem 0 4rem;
  box-shadow: var(--shadow-info);
}

.info-section > .container > p {
  color: var(--color-text-muted);
  max-width: 72ch;
}

.info-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
  margin-top: 2rem;
}

.info-card {
  padding: 1.5rem;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

.info-card:hover {
  border-color: var(--color-card-hover-border);
  box-shadow: var(--shadow-md);
}

.diagram {
  text-align: center;
  margin: 0.5rem 0 1rem;
  padding: 1rem;
  background: var(--color-surface-elevated);
  border-radius: var(--radius-sm);
}

.diagram img {
  max-width: 150px;
  height: auto;
}

.info-card ul {
  margin: 0.5rem 0 1rem;
  padding-left: 1.25rem;
  color: var(--color-text-muted);
}

.info-card p {
  margin: 0.5rem 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

.try-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  margin-top: 0.5rem;
  padding: 0.5rem 1rem;
  background: var(--color-primary);
  color: white !important;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  transition: background 0.15s ease, transform 0.15s ease;
}

.try-link:hover {
  background: var(--color-primary-hover);
  color: white;
  transform: translateY(-1px);
}

.try-link::after {
  content: "→";
}

/* Responsive */
@media (max-width: 900px) {
  .info-grid {
    grid-template-columns: 1fr;
  }

  .inputs-grid {
    grid-template-columns: 1fr;
    gap: 0.75rem;
  }

  .swap-col {
    padding: 0;
  }

  .swap-btn {
    transform: rotate(90deg);
  }

  .swap-btn:hover {
    transform: rotate(270deg);
  }
}

@media (max-width: 600px) {
  .calculator-card {
    padding: 1.25rem;
  }

  .operations {
    flex-direction: column;
  }

  .op-btn {
    min-width: unset;
  }
}