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

html {
  background-color: var(--color-bg);
  height: 100%;
}

body {
  background-color: var(--color-bg);
  height: 100%;
  margin: 0;
  overflow: hidden;
  overscroll-behavior: none;
}

/* === App Shell === */
.app {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  max-width: 430px;
  margin: 0 auto;
  padding-top: env(safe-area-inset-top, 0px);
  background: var(--color-bg);

  font-family: var(--font-ui);
  color: var(--color-text);
  -webkit-font-smoothing: antialiased;

  background-color: var(--color-bg);

  padding-top: env(safe-area-inset-top, 0px);
  padding-left: env(safe-area-inset-left, 0px);
  padding-right: env(safe-area-inset-right, 0px);
}

/* === Header Bar === */
.header-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-2) var(--space-4);
  flex-shrink: 0;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 10px;
}

.header-mark {
  width: 22px;
  height: 22px;
  color: var(--color-text);
  flex-shrink: 0;
}

.app-name {
  font-size: 13px;
  font-weight: 600;
  color: var(--color-text-muted);
  letter-spacing: 2px;
  text-transform: uppercase;
}

.app-name-sub {
  font-weight: 800;
  color: var(--color-accent);
  letter-spacing: 2.5px;
}

.settings-btn {
  width: 44px;
  height: 44px;
  border: none;
  border-radius: var(--radius-md);
  background: transparent;
  color: var(--color-text-muted);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
}

/* === Display === */
.display {
  margin: 0 var(--space-4);
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--display-bg);
  position: relative;
  flex-shrink: 0;
}

.display::after {
  content: '';
  position: absolute;
  top: -1px;
  left: var(--space-4);
  right: var(--space-4);
  height: 2px;
  background: var(--color-accent-strong);
}

.display-equation {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  min-height: 1.4em;
  text-align: right;
}

.display-equation .imperial { color: var(--color-text); }
.display-equation .metric { color: var(--color-metric); }
.display-equation .op { color: var(--color-accent); font-weight: 700; }
.display-equation .recalled { color: var(--color-save); font-weight: 600; }

.display-main {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--display-font-size);
  font-weight: 700;
  color: var(--color-text);
  text-align: right;
  line-height: 1.15;
  min-height: 1.3em;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.display-main .hl { color: var(--color-accent); }
.display-main .approx { color: var(--color-text-muted); }
.display-main .error { color: var(--color-error); }

.display-result {
  display: flex;
  align-items: baseline;
  justify-content: flex-end;
  gap: var(--space-2);
}

.display-unit-label {
  font-size: 10px;
  color: var(--color-accent);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  align-self: flex-start;
  margin-top: 10px;
  opacity: 0.6;
}

.display-conversions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 5px;
  margin-top: var(--space-2);
  padding-top: var(--space-2);
  border-top: 1px solid var(--color-border);
}

.conv-chip {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: 7px 12px;
  min-height: 38px;
  border-radius: var(--radius-md);
  cursor: pointer;
  border: 1.5px solid transparent;
  background: transparent;
  touch-action: manipulation;
}
.conv-chip:active { transform: scale(0.97); }
.conv-chip.imperial { background: var(--color-imperial-dim); border-color: var(--color-imperial-border); }
.conv-chip.metric { background: var(--color-metric-dim); border-color: var(--color-metric-border); }
.chip-unit { font-size: var(--text-xs); font-weight: 700; text-transform: uppercase; letter-spacing: 0.5px; min-width: 26px; }
.conv-chip.imperial .chip-unit { color: var(--color-imperial); }
.conv-chip.metric .chip-unit { color: var(--color-metric); }
.chip-val { font-family: var(--font-mono); font-variant-numeric: tabular-nums; font-size: 15px; font-weight: 700; color: var(--color-text); flex: 1; text-align: right; }

.conversion {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}

.conversion strong {
  color: var(--color-text);
  font-weight: 600;
}

.conversion .unit { color: rgba(65, 135, 255, 0.5); }
.conversion .metric-unit { color: rgba(74, 222, 128, 0.6); }

/* === Fraction Ruler === */
.ruler-container {
  padding: var(--space-2) var(--space-4) 0;
  flex-shrink: 0;
}

.ruler-label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 10px;
  text-transform: uppercase;
  letter-spacing: 1.5px;
  color: var(--color-text-muted);
  font-weight: 600;
  margin-bottom: var(--space-1);
}

.ruler-precision { color: var(--raw-orange-400); font-size: 9px; }

.ruler-coarse {
  display: flex;
  height: 48px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
  background: rgba(65, 135, 255, 0.08);
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}

.ruler-mark {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-end;
  cursor: pointer;
  padding-bottom: 4px;
  position: relative;
  transition: background var(--duration-fast);
}

.ruler-mark:active { background: rgba(65, 135, 255, 0.15); }

.ruler-mark.selected {
  background: rgba(65, 135, 255, 0.2);
}

.ruler-mark.selected::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--color-accent-strong);
}

.ruler-tick {
  width: 1.5px;
  background: rgba(65, 135, 255, 0.5);
  margin-bottom: 3px;
}

.ruler-tick.h1 { height: 20px; background: var(--color-accent); }
.ruler-tick.h2 { height: 13px; }
.ruler-tick.h3 { height: 7px; }

.ruler-lbl {
  font-size: 8px;
  color: var(--color-text-muted);
  font-weight: 600;
  line-height: 1;
}

.ruler-mark.selected .ruler-lbl { color: var(--color-accent); }

/* === Keypad === */
.keypad {
  flex-shrink: 0;
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: var(--key-gap);
  padding: var(--space-2) var(--space-3);
  max-height: 400px;
  transition: max-height 0.25s ease-out, padding 0.25s ease-out, opacity 0.2s;
  overflow: hidden;
}

.keypad.collapsed {
  max-height: 0;
  padding-top: 0;
  padding-bottom: 0;
  opacity: 0;
}

@media (prefers-reduced-motion: reduce) {
  .keypad { transition: none; }
}

.key {
  min-height: var(--key-min-height);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: var(--text-2xl);
  font-weight: 600;
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(65, 135, 255, 0.08);
  color: var(--color-text);
  touch-action: manipulation;
  -webkit-user-select: none;
  user-select: none;
  -webkit-appearance: none;
  appearance: none;
  transition: background var(--duration-fast), transform var(--duration-fast);
}

.key:active {
  transform: scale(0.96);
  background: rgba(65, 135, 255, 0.2);
  border-color: var(--color-accent);
}

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

@media (hover: hover) {
  .key:hover { background: rgba(65, 135, 255, 0.12); }
}

.key-op {
  background: rgba(65, 135, 255, 0.15);
  color: var(--color-accent);
  border-color: rgba(65, 135, 255, 0.3);
  font-weight: 700;
}

.key-op:active { background: rgba(65, 135, 255, 0.3); }
.key-op.active-op { background: var(--color-accent-strong); color: #fff; }

.key-func {
  background: transparent;
  color: var(--color-text-muted);
  font-family: var(--font-ui);
  font-size: var(--text-lg);
}

.key-func:active { background: rgba(65, 135, 255, 0.1); }

/* Unit keys — left column */
.key-unit {
  border: 2px solid var(--color-imperial);
  color: var(--color-imperial);
  background: var(--color-imperial-dim);
  font-family: var(--font-ui);
  font-size: var(--text-lg);
  font-weight: 700;
}
.key-unit:active { background: rgba(255, 152, 0, 0.25); }
.key-unit.key-metric {
  border-color: var(--color-metric);
  color: var(--color-metric);
  background: var(--color-metric-dim);
}
.key-unit.key-metric:active { background: rgba(34, 211, 238, 0.25); }

/* Save key — purple, with hold hint */
.key-save {
  border: 2px solid var(--color-save);
  color: var(--color-save);
  background: var(--color-save-dim);
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  font-weight: 700;
  flex-direction: column;
  gap: 0;
  line-height: 1.1;
  -webkit-touch-callout: none;
  padding: 2px;
}
.key-save:active { background: rgba(167, 139, 250, 0.3); }
.save-hint { font-size: 7px; opacity: 0.45; font-weight: 500; letter-spacing: 0.2px; }

/* Backspace — promoted */
.key-back {
  background: transparent;
  color: var(--color-text);
  font-size: var(--text-xl);
}
.key-back:active { color: var(--color-accent); }

/* Fraction picker key */
.key-frac {
  border: 2px solid var(--color-imperial-border);
  color: var(--color-imperial);
  background: var(--color-imperial-dim);
  font-size: var(--text-2xl);
  font-weight: 600;
}

/* Paren key */
.key-paren {
  font-size: var(--text-xl);
  font-weight: 600;
  color: var(--color-text-muted);
  letter-spacing: 1px;
}

/* Equals */
.key-eq {
  background: var(--color-accent-strong);
  color: #fff;
  border-color: var(--color-accent-strong);
  font-weight: 700;
  font-size: var(--text-3xl);
}
.key-eq:active { background: var(--color-accent); }

/* Label dialog */
.label-overlay {
  position: fixed; inset: 0;
  background: rgba(0, 0, 0, 0.5);
  z-index: 199;
}
.label-overlay[hidden] { display: none; }

.label-dialog {
  position: fixed;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  width: min(320px, 90vw);
  background: var(--color-bg-raised);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-4);
  z-index: 200;
}
.label-dialog[hidden] { display: none; }
.label-dialog h3 { font-size: var(--text-sm); color: var(--color-text); margin-bottom: var(--space-3); font-weight: 700; }
.label-input {
  width: 100%;
  padding: var(--space-2) var(--space-3);
  border: 2px solid var(--color-save-border);
  border-radius: var(--radius-md);
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  margin-bottom: var(--space-3);
}
.label-input:focus { outline: none; border-color: var(--color-save); }
.label-input::placeholder { color: var(--color-text-muted); }
.label-btns { display: flex; gap: var(--space-2); }
.label-btn {
  flex: 1;
  padding: var(--space-2);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: transparent;
  color: var(--color-text-muted);
  font-family: var(--font-ui);
  font-size: var(--text-xs);
  font-weight: 600;
  cursor: pointer;
}
.label-btn.primary { background: var(--color-save); color: #fff; border-color: var(--color-save); }
.label-btn:active { opacity: 0.8; }

/* === Settings Panel === */
.settings-panel {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  max-width: 430px;
  margin: 0 auto;
  background: var(--color-bg);
  border-top: 2px solid var(--color-accent-strong);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  z-index: 100;
  box-shadow: 0 -8px 32px rgba(0, 0, 0, 0.5);
  padding-bottom: env(safe-area-inset-bottom, 0px);
}
.settings-panel[hidden] { display: none; }
.settings-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--color-border);
}
.settings-header h2 { font-size: var(--text-base); font-weight: 700; color: var(--color-text); margin: 0; }
.settings-close {
  width: 28px; height: 28px; border: none; border-radius: var(--radius-sm);
  background: transparent; color: var(--color-text-muted); font-size: var(--text-lg);
  display: flex; align-items: center; justify-content: center; cursor: pointer;
}
.settings-body { padding: var(--space-3) var(--space-4); }
.settings-group { margin-bottom: var(--space-4); }
.settings-label {
  font-size: var(--text-xs); color: var(--color-text-muted); text-transform: uppercase;
  letter-spacing: 1.5px; font-weight: 600; margin-bottom: var(--space-2); display: block;
}
.settings-row { display: flex; gap: var(--space-2); }
.settings-option {
  flex: 1; padding: 8px 4px; border: 1px solid var(--color-border); border-radius: var(--radius-md);
  background: transparent; color: var(--color-text-muted); font-family: var(--font-ui);
  font-size: var(--text-xs); font-weight: 600; cursor: pointer; text-align: center;
}
.settings-option.active {
  border-color: var(--color-accent-strong); color: var(--color-accent);
  background: rgba(65, 135, 255, 0.1);
}
.settings-option:active { opacity: 0.8; }

/* === Tab Bar === */
.tab-bar {
  display: flex;
  background: var(--color-bg-raised);
  border-top: 1px solid var(--color-border);
  padding: 4px 0;
  padding-bottom: calc(4px + env(safe-area-inset-bottom, 0px));
  flex-shrink: 0;
}

.tab {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  padding: 6px 0;
  background: none;
  border: none;
  color: var(--color-text-muted);
  cursor: pointer;
  font-size: 10px;
  font-weight: 600;
  font-family: var(--font-ui);
  letter-spacing: 0.5px;
  text-transform: uppercase;
  touch-action: manipulation;
  -webkit-user-select: none;
  user-select: none;
  position: relative;
}

.tab.active { color: var(--color-accent); }

/* Pill background for active tab */
.tab-pill {
  position: absolute;
  top: 2px;
  left: 50%;
  transform: translateX(-50%);
  width: 48px;
  height: 28px;
  border-radius: 14px;
  background: transparent;
  pointer-events: none;
  transition: background var(--duration-normal);
}

.tab.active .tab-pill {
  background: rgba(65, 135, 255, 0.12);
}

.tab-icon { font-size: 20px; line-height: 1; display: flex; align-items: center; justify-content: center; position: relative; }
.tab-icon svg { width: 20px; height: 20px; fill: none; stroke: currentColor; stroke-width: 2; stroke-linecap: round; stroke-linejoin: round; }

.tab-dot {
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--color-accent-strong);
}

.tab:not(.active) .tab-dot { display: none; }

/* === Coming Soon overlay === */
.tab-panel { display: none; }
.tab-panel.active { display: flex; flex-direction: column; flex: 1; min-height: 0; position: relative; }

.coming-soon {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  font-size: var(--text-lg);
  text-transform: uppercase;
  letter-spacing: 2px;
}

/* === Reduced motion === */
@media (prefers-reduced-motion: reduce) {
  .key { transition: none; }
  .key:active { transform: none; }
  .ruler-mark { transition: none; }
}

/* === Install Banner === */
.install-banner {
  flex-shrink: 0;
  margin: var(--space-1) var(--space-3);
  max-width: 400px;
  margin: 0 auto;
  padding: var(--space-3) var(--space-4);
  background: var(--color-bg-raised);
  border: 1px solid var(--color-accent-strong);
  border-radius: var(--radius-lg);
  color: var(--color-text);
  font-size: var(--text-xs);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2);
}

.install-banner[hidden] { display: none; }

.install-banner strong { color: var(--color-accent); }

.install-dismiss {
  width: 24px;
  height: 24px;
  border: none;
  border-radius: 50%;
  background: transparent;
  color: var(--color-text-muted);
  font-size: var(--text-base);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

/* === Screen reader only === */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}