/* ─── Reset & Base ─── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --label-width: 120px;
  --col-width: 160px;
  --gutter: 40px;
  --margin: 48px;
  --max-width: 600px;

  --color-bg: #f5f4f0;
  --color-text: #1a1a1a;
  --color-text-secondary: #6b6b6b;
  --color-accent: #d63031;
  --color-border: #c8c7c3;

  --font-sans: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ─── Container ─── */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin-inline: auto;
  padding-inline: var(--margin);
}

/* ─── Header ─── */
.header {
  padding-block: 56px 36px;
  border-bottom: 2px solid var(--color-text);
}

.header .container {
  display: flex;
  justify-content: space-between;
  align-items: flex-end;
}

.header__title {
  font-size: 3rem;
  font-weight: 700;
  line-height: 1.05;
  letter-spacing: -0.03em;
  text-transform: uppercase;
}

/* Unit toggle */
.unit-toggle {
  background: none;
  border: 1.5px solid var(--color-border);
  padding: 6px 12px;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 2px;
  transition: border-color 0.15s;
}

.unit-toggle:hover {
  border-color: var(--color-text);
}

.unit-toggle__label {
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  transition: color 0.15s;
  user-select: none;
}

.unit-toggle__label.active {
  color: var(--color-accent);
  font-weight: 700;
}

.unit-toggle__sep {
  color: var(--color-border);
  font-size: 0.8125rem;
  margin-inline: 2px;
}

/* ─── Main ─── */
.main {
  flex: 1;
  padding-block: 40px 48px;
}

/* ─── Shared row grid ─── */
/* Single-column (A only): label | A */
/* With B visible: label | A | B */
.row-labels,
.row {
  display: grid;
  grid-template-columns: var(--label-width) 1fr;
  align-items: center;
  gap: 0 var(--gutter);
}

.row-labels.expanded,
.row.expanded {
  grid-template-columns: var(--label-width) 1fr 1fr;
}

/* Column headers */
.row-labels {
  margin-bottom: 12px;
}

.row-labels__spacer {
  /* occupies label column */
}

.row-labels__col {
  font-size: 0.6875rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-secondary);
  padding-bottom: 8px;
  border-bottom: 1.5px solid var(--color-text);
}

/* ─── Row label ─── */
.row__label {
  font-size: 0.6875rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-text-secondary);
  padding-block: 14px 0;
}

/* ─── Input cells ─── */
.row--input {
  border-bottom: 1px solid var(--color-border);
}

.row--input .row__cell {
  display: flex;
  align-items: center;
  gap: 6px;
  padding-block: 10px;
  border-bottom: none; /* border on the row, not the cell */
}

.row__input {
  background: none;
  border: none;
  outline: none;
  font-family: var(--font-sans);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text);
  width: 100%;
  -moz-appearance: textfield;
}

.row__input::-webkit-inner-spin-button,
.row__input::-webkit-outer-spin-button {
  -webkit-appearance: none;
}

.row__select {
  background: none;
  border: none;
  outline: none;
  font-family: var(--font-sans);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text);
  cursor: pointer;
  appearance: none;
  -webkit-appearance: none;
  width: 100%;
  padding-right: 18px;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='10' height='6' viewBox='0 0 10 6'%3E%3Cpath d='M1 1l4 4 4-4' stroke='%236b6b6b' fill='none' stroke-width='1.5'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0 center;
}

.row__select option {
  font-size: 1rem;
}

.row__unit {
  font-size: 0.8125rem;
  color: var(--color-text-secondary);
  font-weight: 500;
  white-space: nowrap;
}

/* ─── Divider between inputs and results ─── */
.row--divider {
  height: 0;
  border-top: 2px solid var(--color-text);
  margin-block: 4px;
  grid-column: 1 / -1;
}

/* ─── Result rows ─── */
.row:not(.row--input):not(.row--divider):not(.row--tires):not(.compare-row) {
  border-bottom: 1px solid var(--color-border);
}

.row__result {
  font-size: 1.75rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-text);
  padding-block: 12px;
  text-align: left;
}

.row__result--accent {
  color: var(--color-accent);
}

/* patches row gets a heavier bottom border */
.row--patches {
  border-bottom-width: 2px !important;
  border-bottom-color: var(--color-text) !important;
}

/* ─── Tire SVG row ─── */
.row--tires {
  margin-top: 24px;
}

.row__cell--tire {
  display: flex;
  justify-content: flex-start;
  align-items: center;
}

.tire {
  width: 120px;
  height: 120px;
}

/* ─── Compare button ─── */
.compare-row {
  margin-top: 28px;
}

.compare-btn {
  background: none;
  border: 1.5px solid var(--color-border);
  padding: 8px 16px;
  font-family: var(--font-sans);
  font-size: 0.8125rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--color-text-secondary);
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

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

/* ─── Hidden B column (default) ─── */
/* .row--input .row__cell has specificity 0-2-0, so hidden must match or beat it */
.row .row__cell--hidden,
.row .row__result--hidden,
.row-labels .row-labels__col--hidden,
.row-labels--hidden {
  display: none;
}

/* ─── Footer ─── */
.footer {
  padding-block: 20px 32px;
  border-top: 1px solid var(--color-border);
}

.footer__note {
  font-size: 0.6875rem;
  color: var(--color-text-secondary);
  line-height: 1.5;
}

/* ─── Responsive ─── */
@media (max-width: 560px) {
  :root {
    --margin: 20px;
    --label-width: 90px;
    --gutter: 20px;
  }

  .header {
    padding-block: 36px 24px;
  }

  .header__title {
    font-size: 2rem;
  }

  .row__input,
  .row__select {
    font-size: 1.25rem;
  }

  .row__result {
    font-size: 1.5rem;
  }

  .tire {
    width: 100px;
    height: 100px;
  }
}