:root {
  --bg: #ffffff;
  --text: #1d1d1f;
  --secondary: #6e6e73;
  --border: #d2d2d7;
  --card: #f5f5f7;
  --accent: #007aff;
  --accent-pressed: #0062cc;
  --error: #ff3b30;
  --placeholder: #c7c7cc;
  --radius: 14px;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.04), 0 4px 16px rgba(0, 0, 0, 0.04);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "SF Pro Display",
    "Helvetica Neue", Helvetica, Arial, "PingFang HK", "PingFang TC",
    "Hiragino Sans CNS", "Noto Sans TC", sans-serif;
}

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

html,
body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  position: relative;
  min-height: 100dvh;
  line-height: 1.47;
}

.page {
  max-width: 560px;
  margin: 0 auto;
  padding: 48px 24px 64px;
}

.header {
  margin-bottom: 36px;
}

.header h1 {
  margin: 0;
  font-size: 34px;
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.15;
}

.subtitle {
  margin: 8px 0 0;
  color: var(--secondary);
  font-size: 17px;
}

.field-block {
  margin-bottom: 28px;
}

.field-label {
  display: block;
  margin: 0 0 10px;
  font-size: 13px;
  font-weight: 600;
  color: var(--secondary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.segmented {
  display: flex;
  flex-wrap: nowrap;
  gap: 4px;
  padding: 4px;
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.segmented button {
  flex: 1 1 0;
  min-width: 0;
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--secondary);
  font-family: inherit;
  font-size: 15px;
  font-weight: 500;
  padding: 10px 12px;
  border-radius: 10px;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease, box-shadow 0.15s ease;
  -webkit-tap-highlight-color: transparent;
  white-space: nowrap;
  text-align: center;
}

/* 4-chip support control: shorter labels + ~13–14px so it fits 560 without ugly wrap */
.segmented--support button {
  font-size: 13.5px;
  font-weight: 500;
  padding: 9px 6px;
  letter-spacing: -0.01em;
}

.segmented button[aria-pressed="true"] {
  background: #fff;
  color: var(--accent);
  font-weight: 600;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.04);
}

.segmented button:hover:not([aria-pressed="true"]) {
  color: var(--text);
}

.segmented button:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.input-row {
  display: flex;
  gap: 12px;
}

.input-row > .input-group {
  flex: 1;
  min-width: 0;
}

.input-group {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.input-group .mini-label {
  margin: 0;
  font-size: 13px;
  font-weight: 500;
  color: var(--secondary);
}

.input-wrap {
  display: flex;
  align-items: center;
  gap: 8px;
  background: var(--card);
  border: 1px solid transparent;
  border-radius: var(--radius);
  padding: 14px 16px;
  transition: border-color 0.15s ease, box-shadow 0.15s ease, background 0.15s ease;
  box-shadow: var(--shadow);
}

.input-wrap:focus-within {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(0, 122, 255, 0.15);
  background: #fff;
}

.input-wrap input {
  flex: 1;
  border: 0;
  outline: 0;
  background: transparent;
  font-size: 22px;
  font-weight: 600;
  letter-spacing: -0.02em;
  color: var(--text);
  width: 100%;
  min-width: 0;
  font-variant-numeric: tabular-nums;
  font-family: inherit;
}

.input-wrap input::placeholder {
  color: var(--placeholder);
  font-weight: 500;
}

.unit-suffix {
  flex-shrink: 0;
  font-size: 15px;
  font-weight: 500;
  color: var(--secondary);
  font-variant-numeric: tabular-nums;
}

/* —— Multi-load row stacks —— */
.load-rows {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.load-row {
  display: flex;
  align-items: flex-start;
  gap: 8px;
}

.load-row > .input-row {
  flex: 1;
  min-width: 0;
}

.btn-remove {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--secondary);
  font-family: inherit;
  font-size: 22px;
  font-weight: 300;
  line-height: 1;
  padding: 0;
  margin-top: 30px; /* align with input shell under mini-label */
  width: 32px;
  height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  border-radius: 8px;
  flex-shrink: 0;
  -webkit-tap-highlight-color: transparent;
  transition: color 0.15s ease, background 0.15s ease;
}

.btn-remove:hover,
.btn-remove:focus-visible {
  color: var(--error);
  background: rgba(255, 59, 48, 0.08);
  outline: none;
}

.btn-remove[hidden] {
  display: none;
}

.btn-add {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--accent);
  font-family: inherit;
  font-size: 15px;
  font-weight: 500;
  padding: 8px 0 0;
  margin-top: 4px;
  cursor: pointer;
  text-align: left;
  -webkit-tap-highlight-color: transparent;
  transition: color 0.15s ease;
}

.btn-add:hover,
.btn-add:focus-visible {
  color: var(--accent-pressed);
  outline: none;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.btn-add:disabled,
.btn-add[hidden] {
  display: none;
}

.cards {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.card {
  background: var(--card);
  border-radius: var(--radius);
  padding: 18px 18px 20px;
  box-shadow: var(--shadow);
}

.card-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 12px;
}

.card-head h2 {
  margin: 0;
  font-size: 13px;
  font-weight: 600;
  color: var(--secondary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.diagram-card {
  padding-bottom: 16px;
}

.diagram-svg {
  display: block;
  width: 100%;
  height: auto;
  margin-bottom: 16px;
  background: #fff;
  border-radius: 10px;
}

.strip-label {
  margin: 0 0 6px;
  font-size: 12px;
  font-weight: 600;
  color: var(--secondary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.strip-svg {
  display: block;
  width: 100%;
  height: auto;
  margin-bottom: 12px;
  background: #fff;
  border-radius: 8px;
}

.strip-svg:last-child {
  margin-bottom: 0;
}

.results {
  display: flex;
  flex-direction: column;
  gap: 16px;
  margin-top: 4px;
}

/* Reactions: default 2-up (SS Ra/Rb, Cantilever V/M) */
.reaction-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

/* Fixed–pin: Va | Vb on top, Ma full-width below (2+1) */
.reaction-grid--triple {
  grid-template-columns: 1fr 1fr;
}

.reaction-grid--triple .reaction-item:nth-child(3) {
  grid-column: 1 / -1;
}

/* Fixed–fixed: Va Vb / Ma Mb — 2×2 */
.reaction-grid--quad {
  grid-template-columns: 1fr 1fr;
}

.reaction-item {
  min-width: 0;
}

.reaction-label {
  display: block;
  margin: 0 0 6px;
  font-size: 13px;
  font-weight: 500;
  color: var(--secondary);
}

.reaction-hint {
  font-weight: 400;
  color: var(--secondary);
  opacity: 0.85;
}

.output {
  margin: 0;
  font-size: 22px;
  font-weight: 600;
  letter-spacing: -0.01em;
  line-height: 1.4;
  word-break: break-word;
  min-height: 1.4em;
  color: var(--text);
  font-variant-numeric: tabular-nums;
}

.output.is-empty,
.output.is-na {
  color: var(--placeholder);
  font-weight: 500;
}

.footer-note {
  margin: 36px 0 0;
  text-align: center;
  font-size: 13px;
  color: var(--secondary);
  line-height: 1.4;
}

.home-link {
  position: absolute;
  top: max(16px, env(safe-area-inset-top, 0px));
  left: max(16px, env(safe-area-inset-left, 0px));
  z-index: 10;
  display: inline-flex;
  align-items: center;
  gap: 2px;
  min-width: 44px;
  min-height: 44px;
  padding: 10px 10px 10px 6px;
  box-sizing: border-box;
  font-size: 17px;
  font-weight: 400;
  line-height: 1.2;
  letter-spacing: -0.01em;
  color: #6e6e73;
  text-decoration: none;
  -webkit-tap-highlight-color: transparent;
}

.home-link:hover,
.home-link:focus-visible {
  color: #007aff;
  outline: none;
}

.home-chevron {
  font-size: 22px;
  font-weight: 300;
  line-height: 1;
  transform: translateY(-0.5px);
}

@media (max-width: 480px) {
  .page {
    padding: 36px 20px 48px;
  }

  .header h1 {
    font-size: 28px;
  }

  .input-wrap input {
    font-size: 19px;
  }

  .output {
    font-size: 19px;
  }

  .input-row {
    flex-direction: column;
    gap: 16px;
  }

  .load-row {
    flex-direction: column;
    gap: 4px;
  }

  .btn-remove {
    margin-top: 0;
    align-self: flex-end;
    height: 36px;
  }

  /* Support chips: keep equal flex; wrap only as last resort with same gap */
  .segmented--support {
    flex-wrap: wrap;
  }

  .segmented--support button {
    flex: 1 1 calc(50% - 4px);
    font-size: 13px;
    padding: 9px 8px;
  }

  /* Keep reaction grids 2-col on phone (SS/Cant 2-up, FP 2+1, FF 2×2) */
  .reaction-grid,
  .reaction-grid--triple,
  .reaction-grid--quad {
    grid-template-columns: 1fr 1fr;
    gap: 12px;
  }

  .reaction-grid--triple .reaction-item:nth-child(3) {
    grid-column: 1 / -1;
  }
}