:root {
  /* Design tokens shadcn/ui — palette "zinc", radius e ombre verificati dai
     sorgenti del pacchetto (default_theme_variant.dart, shadows.dart,
     color_scheme/zinc.dart) */
  --background: #ffffff;
  --foreground: #09090b;
  --card: #ffffff;
  --card-foreground: #09090b;
  --primary: #18181b;
  --primary-foreground: #fafafa;
  --secondary: #f4f4f5;
  --secondary-foreground: #18181b;
  --muted: #f4f4f5;
  --muted-foreground: #71717a;
  --accent: #f4f4f5;
  --accent-foreground: #18181b;
  --destructive: #ef4444;
  --destructive-bg: #fef2f2;
  --border: #e4e4e7;
  --input: #e4e4e7;
  --ring: #18181b;

  --radius: 0.5rem;
  --radius-sm: calc(var(--radius) - 4px);
  --radius-md: calc(var(--radius) - 2px);
  --radius-lg: var(--radius);

  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);

  --font-sans: "Google Sans Flex", ui-sans-serif, system-ui, -apple-system,
    "Segoe UI", Roboto, sans-serif;

  --max-width: 860px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 15px;
  background: var(--background);
  color: var(--foreground);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

.site-header {
  padding: 2.5rem 1rem 1.25rem;
  text-align: center;
}

.site-header h1 {
  margin: 0 0 0.3rem;
  font-size: 1.75rem;
  font-weight: 600;
  letter-spacing: -0.02em;
}

.subtitle {
  margin: 0;
  color: var(--muted-foreground);
  font-size: 0.9375rem;
}

main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1rem 2rem;
}

.card {
  background: var(--card);
  color: var(--card-foreground);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  padding: 1.5rem;
  margin-top: 1.5rem;
}

.card h2 {
  margin-top: 0;
  font-size: 1.05rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.field {
  margin-bottom: 1.25rem;
}

.divider {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin: 1.5rem 0;
  color: var(--muted-foreground);
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.divider::before, .divider::after {
  content: "";
  flex: 1 1 auto;
  height: 1px;
  background: var(--border);
}

.field label {
  display: block;
  font-weight: 500;
  font-size: 0.875rem;
  margin-bottom: 0.4rem;
}

.optional {
  font-weight: 400;
  color: var(--muted-foreground);
}

input[type="text"], select {
  width: 100%;
  height: 2.5rem;
  padding: 0 0.75rem;
  border: 1px solid var(--input);
  border-radius: var(--radius-md);
  font-family: var(--font-sans);
  font-size: 0.875rem;
  background: var(--background);
  color: var(--foreground);
  transition: box-shadow 0.15s ease, border-color 0.15s ease;
}

select {
  appearance: none;
  -webkit-appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%2371717a' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.65rem center;
  background-size: 1rem;
  padding-right: 2.25rem;
}

input[type="text"]:focus-visible, select:focus-visible {
  outline: none;
  border-color: var(--ring);
  box-shadow: 0 0 0 3px rgb(24 24 27 / 0.12);
}

.hint {
  margin: 0.4rem 0 0;
  font-size: 0.8125rem;
  color: var(--muted-foreground);
}

.math-input-row {
  display: flex;
  align-items: stretch;
  gap: 0.5rem;
}

math-field {
  flex: 1 1 auto;
  min-width: 0;
  border: 1px solid var(--input);
  border-radius: var(--radius-md);
  padding: 0.6rem 0.75rem;
  font-size: 1.1rem;
  background: var(--background);
  --caret-color: var(--primary);
  transition: box-shadow 0.15s ease, border-color 0.15s ease;
}

math-field:focus-within {
  outline: none;
  border-color: var(--ring);
  box-shadow: 0 0 0 3px rgb(24 24 27 / 0.12);
}


.banner {
  padding: 0.85rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: var(--muted);
  color: var(--foreground);
  margin-bottom: 1rem;
  font-size: 0.875rem;
}

.banner-error {
  background: var(--destructive-bg);
  border-color: rgb(239 68 68 / 0.35);
  color: var(--destructive);
}

.btn-primary, .btn-secondary {
  height: 2.5rem;
  border-radius: var(--radius-md);
  padding: 0 1rem;
  font-family: var(--font-sans);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: background-color 0.15s ease, border-color 0.15s ease, opacity 0.15s ease;
}

.btn-primary:focus-visible, .btn-secondary:focus-visible {
  outline: none;
  box-shadow: 0 0 0 3px rgb(24 24 27 / 0.18);
}

.btn-primary {
  background: var(--primary);
  color: var(--primary-foreground);
  border: 1px solid var(--primary);
}

.btn-primary:hover { opacity: 0.9; }

.reveal-btn {
  display: block;
  margin: 0.5rem 0 0.25rem;
}

.answer-box {
  margin-top: 0.75rem;
  padding: 0.85rem 1rem;
  background: var(--secondary);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
}

.answer-box p {
  margin: 0 0 0.5rem;
}

.answer-box p:last-child {
  margin-bottom: 0;
}

.btn-secondary {
  background: var(--background);
  color: var(--foreground);
  border: 1px solid var(--input);
}

.btn-secondary:hover { background: var(--accent); }

/* funzione studiata, sempre visibile in cima a ogni passo */
.function-display {
  margin-bottom: 1.25rem;
  padding: 0.5rem 1rem;
  background: var(--muted);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  overflow-x: auto;
}

.function-display .katex-display {
  margin: 0.25rem 0;
}

.condition-list {
  margin: 0.5rem 0 0.75rem;
  padding-left: 1.4rem;
}

.condition-list li {
  margin-bottom: 0.45rem;
}

.condition-label {
  font-weight: 500;
}

.condition-note {
  font-size: 0.8125rem;
  color: var(--muted-foreground);
}

.step-content h2 {
  margin-top: 0;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.step-body-section {
  margin-bottom: 1rem;
}

.step-body-section h3 {
  font-size: 0.8125rem;
  font-weight: 500;
  margin: 0 0 0.35rem;
  color: var(--muted-foreground);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.katex-display-block {
  overflow-x: auto;
  padding: 0.25rem 0;
}

#graph-wrap {
  position: relative;
  margin: 1.25rem 0;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 0.75rem;
}

#graph {
  width: 100%;
  max-width: 100%;
  overflow-x: auto;
}

/* frecce "tende a ±∞" agli angoli del grafico: ancorate al riquadro (non ai
   dati di function-plot), restano quindi sempre al bordo visibile a ogni
   livello di zoom/pan. */
.graph-trend {
  position: absolute;
  font-size: 0.85rem;
  font-weight: 600;
  color: #1c7ed6;
  background: color-mix(in srgb, var(--card) 85%, transparent);
  padding: 0.1rem 0.35rem;
  border-radius: var(--radius-sm);
  pointer-events: none;
}

.graph-trend-tl { top: 0.5rem; left: 0.5rem; }
.graph-trend-tr { top: 0.5rem; right: 0.5rem; }
.graph-trend-bl { bottom: 0.5rem; left: 0.5rem; }
.graph-trend-br { bottom: 0.5rem; right: 0.5rem; }

.step-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin-top: 1.5rem;
  justify-content: space-between;
}

.step-nav button {
  flex: 1 1 auto;
}

.site-footer {
  text-align: center;
  color: var(--muted-foreground);
  font-size: 0.8125rem;
  padding: 1.5rem 1rem;
}

@media (max-width: 480px) {
  .site-header h1 { font-size: 1.4rem; }
  .card { padding: 1rem; }
  .step-nav { flex-direction: column; }
}