/* ==========================================================================
   Custom properties
   ========================================================================== */
:root {
  /* Kleuren */
  --color-bg: #f6f7f9;
  --color-surface: #ffffff;
  --color-text: #15191e;
  --color-muted: #5d6673;
  --color-border: #e1e5ea;
  --color-grid: #eceff3;
  --color-accent: #2563eb;
  --color-accent-contrast: #ffffff;
  --color-ref: #9aa3ae;
  --color-positive: #15803d;
  --color-negative: #b91c1c;
  --color-focus: #f59e0b;

  /* Typografie */
  --font-sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.25rem;
  --font-size-xl: clamp(2rem, 6vw, 2.75rem);

  /* Ruimte & vorm */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --radius: 0.75rem;
  --radius-sm: 0.5rem;
  --shadow: 0 1px 2px rgb(0 0 0 / 0.04), 0 4px 16px rgb(0 0 0 / 0.04);

  /* Slider */
  --track-height: 0.5rem;
  --thumb-size: 1.5rem;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #111418;
    --color-surface: #1a1e24;
    --color-text: #eef1f4;
    --color-muted: #9aa3ae;
    --color-border: #2a3039;
    --color-grid: #232931;
    --color-accent: #60a5fa;
    --color-accent-contrast: #0b1220;
    --color-ref: #5d6673;
    --color-positive: #4ade80;
    --color-negative: #f87171;
    --shadow: none;
  }
}

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

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: var(--font-size-base);
  line-height: 1.5;
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
}

h1,
h2,
p,
dl,
dd,
figure {
  margin: 0;
}

:focus-visible {
  outline: 3px solid var(--color-focus);
  outline-offset: 2px;
}

main:focus {
  outline: none;
}

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

/* Skip link: alleen zichtbaar bij focus */
.skip-link {
  position: absolute;
  top: var(--space-2);
  left: var(--space-2);
  z-index: 10;
  padding: var(--space-2) var(--space-4);
  color: var(--color-accent-contrast);
  background: var(--color-accent);
  border-radius: var(--radius-sm);
  transform: translateY(-200%);
}

.skip-link:focus {
  transform: none;
}

/* ==========================================================================
   Header & layout (mobile first)
   ========================================================================== */
.site-header {
  padding: var(--space-5) var(--space-4) var(--space-3);
  max-width: 75rem;
  margin-inline: auto;
}

.site-header__title {
  font-size: var(--font-size-lg);
}

.site-header__formula {
  color: var(--color-muted);
  font-size: var(--font-size-sm);
}

.layout {
  display: grid;
  gap: var(--space-4);
  padding: 0 var(--space-4) var(--space-6);
  max-width: 75rem;
  margin-inline: auto;
}

.panel {
  padding: var(--space-4);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.panel__title {
  margin-bottom: var(--space-3);
  font-size: var(--font-size-base);
}

/* ==========================================================================
   Sliders
   ========================================================================== */
.control + .control {
  margin-top: var(--space-5);
}

.control__head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-2);
}

.control__head label {
  font-size: var(--font-size-sm);
  color: var(--color-muted);
}

/* Getalveld met optioneel € of % ervoor/erachter */
.field {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  flex-shrink: 0;
  min-height: 2.75rem;
  padding-inline: var(--space-3);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
}

.field:focus-within {
  border-color: var(--color-accent);
  outline: 3px solid var(--color-focus);
  outline-offset: 1px;
}

.field__input {
  width: 5.5ch;
  padding: 0;
  /* Minimaal 16px voorkomt automatisch inzoomen op iOS */
  font: inherit;
  font-size: max(1rem, 16px);
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  text-align: right;
  color: var(--color-text);
  background: transparent;
  border: 0;
}

.field__input:focus {
  outline: none;
}

.field__affix {
  color: var(--color-muted);
  font-size: var(--font-size-sm);
}

.field:has(.field__input[aria-invalid="true"]) {
  border-color: var(--color-negative);
}

.control__scale {
  display: flex;
  justify-content: space-between;
  font-size: 0.75rem;
  color: var(--color-muted);
}

/* Range-input: --fill wordt door JS gezet (0%–100%) */
input[type="range"] {
  --fill: 50%;
  width: 100%;
  height: var(--thumb-size);
  margin: 0;
  background: transparent;
  cursor: pointer;
  -webkit-appearance: none;
  appearance: none;
}

input[type="range"]::-webkit-slider-runnable-track {
  height: var(--track-height);
  border-radius: 999px;
  background: linear-gradient(
    to right,
    var(--color-accent) 0 var(--fill),
    var(--color-border) var(--fill) 100%
  );
}

input[type="range"]::-moz-range-track {
  height: var(--track-height);
  border-radius: 999px;
  background: var(--color-border);
}

input[type="range"]::-moz-range-progress {
  height: var(--track-height);
  border-radius: 999px;
  background: var(--color-accent);
}

input[type="range"]::-webkit-slider-thumb {
  width: var(--thumb-size);
  height: var(--thumb-size);
  margin-top: calc((var(--track-height) - var(--thumb-size)) / 2);
  border: 3px solid var(--color-surface);
  border-radius: 50%;
  background: var(--color-accent);
  box-shadow: 0 1px 4px rgb(0 0 0 / 0.3);
  -webkit-appearance: none;
  appearance: none;
}

input[type="range"]::-moz-range-thumb {
  width: var(--thumb-size);
  height: var(--thumb-size);
  border: 3px solid var(--color-surface);
  border-radius: 50%;
  background: var(--color-accent);
  box-shadow: 0 1px 4px rgb(0 0 0 / 0.3);
}

/* ==========================================================================
   Knoppen
   ========================================================================== */
.actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-5);
}

.button {
  min-height: 2.75rem;
  padding: var(--space-2) var(--space-4);
  font: inherit;
  font-size: var(--font-size-sm);
  font-weight: 600;
  color: var(--color-text);
  background: transparent;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  cursor: pointer;
}

.button:hover {
  border-color: var(--color-muted);
}

.button--primary {
  color: var(--color-accent-contrast);
  background: var(--color-accent);
  border-color: var(--color-accent);
}

.button--primary:hover {
  filter: brightness(1.08);
}

/* ==========================================================================
   Resultaat
   ========================================================================== */
.result__main {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: var(--space-2);
}

.result__value {
  font-size: var(--font-size-xl);
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  line-height: 1.1;
  color: var(--color-accent);
}

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

.stats {
  display: grid;
  gap: var(--space-3);
  margin-top: var(--space-4);
}

.stats__item {
  display: flex;
  justify-content: space-between;
  gap: var(--space-2);
  padding-top: var(--space-3);
  border-top: 1px solid var(--color-border);
}

.stats dt {
  font-size: var(--font-size-sm);
  color: var(--color-muted);
}

.stats dd {
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  text-align: right;
}

.delta--positive {
  color: var(--color-positive);
}

.delta--negative {
  color: var(--color-negative);
}

/* ==========================================================================
   Grafiek
   ========================================================================== */
.chart__canvas {
  display: block;
  width: 100%;
  aspect-ratio: 4 / 3;
}

.legend {
  display: flex;
  gap: var(--space-4);
  margin-top: var(--space-2);
  font-size: var(--font-size-sm);
  color: var(--color-muted);
}

.legend__item {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
}

.legend__swatch {
  width: 1.25rem;
  height: 0;
  border-top: 3px solid var(--color-accent);
}

.legend__swatch--ref {
  border-top: 2px dashed var(--color-ref);
}

.chart__hint {
  margin-top: var(--space-3);
  font-size: var(--font-size-sm);
  color: var(--color-muted);
}

/* ==========================================================================
   Breakpoints
   ========================================================================== */
@media (min-width: 48rem) {
  .site-header,
  .layout {
    padding-inline: var(--space-6);
  }

  .site-header__title {
    font-size: 1.5rem;
  }

  /* Links invoer + resultaat, rechts de grafiek */
  .layout {
    grid-template-columns: minmax(18rem, 22rem) 1fr;
    grid-template-areas:
      "controls chart"
      "result   chart";
    align-items: start;
  }

  .controls { grid-area: controls; }
  .result   { grid-area: result; }
  .chart    { grid-area: chart; }

  .chart__canvas {
    aspect-ratio: 16 / 10;
  }
}

@media (prefers-reduced-motion: reduce) {
  * {
    scroll-behavior: auto !important;
  }
}