/* ===================================================================
   LabCalc Modern Design System
   Light theme, Roboto font, CSS Grid layout, iPhone-optimized
   =================================================================== */

/* --- CSS Custom Properties --- */
:root {
  /* Colors - Light Theme */
  --bg-primary: #f5f5f5;
  --bg-secondary: white;
  --bg-display: white;
  --text-primary: #333;
  --text-display: #333;
  --text-stack: #666;
  --text-secondary: #555;
  --text-label: #666;

  /* Button colors - flat neutral grays */
  --btn-number: #ffffff;
  --btn-number-active: #e0e0e0;
  --btn-function: #d0d0d0;
  --btn-function-active: #b0b0b0;

  /* Accent color (customizable per theme) */
  --accent: #2196F3;
  --accent-hover: #1976D2;
  --accent-success: #2e7d32;

  /* Borders and surfaces */
  --border: #ddd;
  --surface: #f8f9fa;

  /* Radii */
  --radius-sm: 12px;
  --radius-md: 14px;
  --radius-lg: 16px;

  /* Spacing */
  --gap: 6px;
  --pad: 12px;

  /* Typography */
  --font-display: 'Roboto', sans-serif;
  --font-ui: 'Roboto', sans-serif;
  --font-size-display: 32px;
  --font-size-stack: 15px;
  --font-size-btn: 16px;
  --font-size-btn-small: 13px;
  --font-size-label: 11px;
  --font-size-status: 12px;

  /* Safe areas for iPhone notch / home indicator */
  --safe-top: env(safe-area-inset-top, 0px);
  --safe-bottom: env(safe-area-inset-bottom, 0px);
  --safe-left: env(safe-area-inset-left, 0px);
  --safe-right: env(safe-area-inset-right, 0px);
}

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

html {
  height: 100%;
  -webkit-text-size-adjust: 100%;
}

body {
  height: 100%;
  font-family: var(--font-ui);
  background: var(--bg-primary);
  color: var(--text-primary);
  overflow: hidden;
  -webkit-user-select: none;
  user-select: none;
  -webkit-touch-callout: none;
  -webkit-tap-highlight-color: transparent;
}

/* --- Main Calculator Container --- */
.calculator {
  display: grid;
  grid-template-rows: auto 1fr auto auto auto;
  height: 100dvh;
  max-width: 430px;
  margin: 0 auto;
  padding: var(--safe-top) var(--safe-right) 0 var(--safe-left);
  overflow: hidden;
}

/* --- Status Bar --- */
.status-bar {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px var(--pad);
  background: var(--bg-primary);
}

.status-pill {
  appearance: none;
  border: none;
  border-radius: 12px;
  background: var(--btn-number);
  color: var(--text-secondary);
  font-family: var(--font-ui);
  font-size: var(--font-size-status);
  font-weight: 500;
  padding: 4px 10px;
  cursor: pointer;
  transition: background-color 0.15s;
  white-space: nowrap;
}

.status-pill:active {
  background: var(--btn-number-active);
}

.status-spacer {
  flex: 1;
}

.status-pill--icon {
  padding: 3px 8px;
  font-size: 14px;
  line-height: 1;
}

/* --- Display Area --- */
.display {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  padding: 8px var(--pad) 6px;
  background: var(--bg-display);
  min-height: 140px;
}

.stack-entry {
  font-family: var(--font-display);
  font-size: var(--font-size-stack);
  font-weight: 300;
  color: var(--text-stack);
  text-align: right;
  padding: 2px 4px;
  min-height: 22px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  cursor: pointer;
  border-radius: 4px;
  transition: background-color 0.15s;
}

.stack-entry:hover {
  background: var(--surface);
}

.stack-entry:empty {
  min-height: 22px;
}

.display-input {
  appearance: none;
  border: none;
  outline: none;
  background: transparent;
  font-family: var(--font-display);
  font-size: var(--font-size-display);
  font-weight: 300;
  color: var(--text-display);
  text-align: right;
  width: 100%;
  padding: 4px 4px 2px;
  caret-color: var(--accent);
}

/* --- Keypad Sections --- */
.keypad {
  display: grid;
  gap: var(--gap);
  padding: var(--gap) var(--gap) 0;
}

.keypad--functions {
  grid-template-columns: repeat(7, 1fr);
  padding-top: var(--gap);
  background: var(--bg-primary);
}

.keypad--main {
  grid-template-columns: repeat(7, 1fr);
  background: var(--bg-primary);
}

.keypad--enter {
  padding: var(--gap) var(--gap) var(--gap);
  padding-bottom: calc(var(--gap) + var(--safe-bottom));
  background: var(--bg-primary);
}

/* --- Buttons --- */
.btn {
  appearance: none;
  border: none;
  outline: none;
  border-radius: var(--radius-sm);
  font-family: var(--font-ui);
  font-size: var(--font-size-btn);
  font-weight: 500;
  color: var(--text-primary);
  background: var(--btn-number);
  padding: 14px 0;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background-color 0.15s;
  position: relative;
  overflow: hidden;
  line-height: 1.2;
  min-height: 44px;
}

.btn:active,
.btn.btn--active {
  background: var(--btn-number-active);
}

/* Small function buttons (inverse trig, trig rows) */
.btn--small {
  padding: 8px 0;
  font-size: var(--font-size-btn-small);
  min-height: 36px;
}

/* Button type colors */
.btn--number {
  background: var(--btn-number);
}
.btn--number:active,
.btn--number.btn--active {
  background: var(--btn-number-active);
}

.btn--operator {
  background: var(--btn-function);
  font-size: 18px;
  font-weight: 500;
}
.btn--operator:active,
.btn--operator.btn--active {
  background: var(--btn-function-active);
}

.btn--function {
  background: var(--btn-function);
}
.btn--function:active,
.btn--function.btn--active {
  background: var(--btn-function-active);
}

.btn--action {
  background: var(--btn-function);
}
.btn--action:active,
.btn--action.btn--active {
  background: var(--btn-function-active);
}

/* Enter button - full width, accent color */
.btn--enter {
  background: var(--accent);
  color: white;
  font-size: 16px;
  font-weight: 700;
  letter-spacing: 2px;
  padding: 16px 0;
  border-radius: var(--radius-md);
  min-height: 52px;
}
.btn--enter:active,
.btn--enter.btn--active {
  background: var(--accent-hover);
}

/* Superscript text in buttons */
.btn sup {
  font-size: 0.65em;
  vertical-align: super;
  line-height: 0;
}

/* --- Settings Overlay --- */
.settings-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.3);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 200;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

.settings-overlay[hidden] {
  display: none;
}

.settings-panel {
  background: var(--bg-secondary);
  border-radius: var(--radius-lg);
  padding: 24px;
  width: calc(100% - 48px);
  max-width: 360px;
  max-height: 80vh;
  overflow-y: auto;
}

.settings-panel h2 {
  font-size: 20px;
  font-weight: 700;
  margin-bottom: 20px;
  color: var(--text-primary);
}

.setting-group {
  margin-bottom: 20px;
}

.setting-group label {
  display: block;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 8px;
}

.setting-options {
  display: flex;
  gap: 6px;
}

.setting-opt {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-ui);
  font-size: 14px;
  font-weight: 500;
  padding: 8px 14px;
  cursor: pointer;
  flex: 1;
  text-align: center;
  transition: all 0.15s;
}

.setting-opt.active {
  background: var(--accent);
  color: #ffffff;
  border-color: var(--accent);
}

.precision-input {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 16px;
  padding: 8px 12px;
  width: 60px;
  margin-top: 8px;
  text-align: center;
  outline: none;
}

.precision-input:focus {
  border-color: var(--accent);
}

.theme-swatches {
  display: flex;
  gap: 8px;
}

.swatch {
  appearance: none;
  border: 3px solid transparent;
  border-radius: 50%;
  width: 36px;
  height: 36px;
  cursor: pointer;
  transition: border-color 0.15s;
}

.swatch:active {
  transform: scale(0.9);
}

.swatch.active {
  border-color: var(--text-primary);
}

.settings-done {
  appearance: none;
  border: none;
  border-radius: var(--radius-md);
  background: var(--accent);
  color: #ffffff;
  font-family: var(--font-ui);
  font-size: 16px;
  font-weight: 700;
  padding: 12px;
  width: 100%;
  cursor: pointer;
  margin-top: 8px;
}

.settings-done:active {
  opacity: 0.8;
}

/* --- Palette (Bottom Sheet) --- */
.palette {
  position: fixed;
  inset: auto 0 0 0;
  max-height: 75vh;
  background: var(--bg-secondary);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  transform: translateY(100%);
  transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  z-index: 100;
  display: flex;
  flex-direction: column;
  border-top: 1px solid var(--border);
}

.palette--open {
  transform: translateY(0);
}

.palette-handle {
  width: 36px;
  height: 4px;
  background: rgba(0, 0, 0, 0.15);
  border-radius: 2px;
  margin: 10px auto 6px;
  flex-shrink: 0;
}

.palette-tabs {
  display: flex;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.palette-tab {
  appearance: none;
  border: none;
  border-bottom: 2px solid transparent;
  background: none;
  color: var(--text-secondary);
  font-family: var(--font-ui);
  font-size: 13px;
  font-weight: 500;
  padding: 10px 0;
  flex: 1;
  cursor: pointer;
  text-align: center;
  transition: color 0.15s, border-color 0.15s;
}

.palette-tab--active {
  color: var(--accent);
  border-bottom-color: var(--accent);
  font-weight: 700;
}

.palette-content {
  flex: 1;
  overflow-y: auto;
  padding: var(--pad);
  padding-bottom: calc(var(--pad) + var(--safe-bottom));
  -webkit-overflow-scrolling: touch;
}

/* --- Palette: Unit Converter --- */
.unit-category-tabs {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 4px;
  margin-bottom: 12px;
}

.unit-cat-btn {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-primary);
  color: var(--text-secondary);
  font-family: var(--font-ui);
  font-size: 11px;
  font-weight: 500;
  padding: 6px 2px;
  cursor: pointer;
  text-align: center;
  transition: all 0.15s;
}

.unit-cat-btn.active {
  background: var(--accent);
  color: #ffffff;
  border-color: var(--accent);
}

.unit-row {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 6px 0;
  border-bottom: 1px solid var(--border);
}

.unit-label {
  font-size: 12px;
  font-weight: 500;
  color: var(--text-secondary);
  width: 50px;
  flex-shrink: 0;
  text-align: right;
}

.unit-input {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 14px;
  padding: 6px 8px;
  flex: 1;
  min-width: 0;
  outline: none;
}

.unit-input:focus {
  border-color: var(--accent);
}

.unit-name {
  font-size: 11px;
  color: var(--text-secondary);
  width: 80px;
  flex-shrink: 0;
}

.unit-pop-btn {
  appearance: none;
  border: none;
  background: var(--accent);
  color: #ffffff;
  border-radius: 6px;
  width: 22px;
  height: 22px;
  font-size: 12px;
  font-weight: 700;
  cursor: pointer;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* --- Palette: Constants --- */
.const-display {
  background: var(--bg-primary);
  border-radius: var(--radius-sm);
  padding: 10px 12px;
  margin-bottom: 12px;
  min-height: 36px;
}

.const-value {
  font-family: var(--font-display);
  font-size: 16px;
  font-weight: 400;
  color: var(--text-primary);
}

.const-units {
  font-size: 13px;
  color: var(--text-secondary);
  margin-left: 8px;
}

.const-list {
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.const-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 10px;
  border-radius: 8px;
  cursor: pointer;
  transition: background-color 0.15s;
}

.const-item:nth-child(odd) {
  background: var(--bg-primary);
}

.const-item:active {
  background: var(--border);
}

.const-symbol {
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 700;
  color: var(--accent);
  width: 36px;
  text-align: center;
  flex-shrink: 0;
}

.const-name {
  font-size: 13px;
  color: var(--text-primary);
  flex: 1;
}

/* --- Palette: Solver --- */
.solver-section-title {
  font-size: 14px;
  font-weight: 700;
  color: var(--text-primary);
  margin: 12px 0 8px;
}

.solver-section-title:first-child {
  margin-top: 0;
}

.solver-option {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: background-color 0.15s;
  border-bottom: 1px solid var(--border);
}

.solver-option:active {
  background: var(--bg-primary);
}

.solver-option-indicator {
  width: 4px;
  height: 28px;
  border-radius: 2px;
  background: var(--accent);
  flex-shrink: 0;
}

.solver-option-label {
  font-size: 14px;
  color: var(--text-primary);
}

/* Solver Matrix */
.solver-matrix {
  margin: 12px 0;
}

.solver-row {
  display: flex;
  gap: 4px;
  margin-bottom: 4px;
}

.solver-cell {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 13px;
  padding: 6px;
  width: 100%;
  min-width: 0;
  text-align: center;
  outline: none;
}

.solver-cell:focus {
  border-color: var(--accent);
}

.solver-cell--b {
  border-color: var(--accent);
}

.solver-results {
  margin-top: 12px;
}

.solver-result-row {
  display: flex;
  align-items: center;
  padding: 8px 10px;
  border-radius: 8px;
  cursor: pointer;
}

.solver-result-row:nth-child(odd) {
  background: var(--bg-primary);
}

.solver-result-label {
  font-size: 13px;
  font-weight: 700;
  color: var(--accent);
  width: 40px;
}

.solver-result-value {
  font-family: var(--font-display);
  font-size: 14px;
  color: var(--text-primary);
}

.solver-buttons {
  display: flex;
  gap: 8px;
  margin-top: 16px;
}

.solver-btn {
  appearance: none;
  border: none;
  border-radius: var(--radius-sm);
  font-family: var(--font-ui);
  font-size: 14px;
  font-weight: 700;
  padding: 10px 0;
  cursor: pointer;
  flex: 1;
  text-align: center;
}

.solver-btn--solve {
  background: var(--accent);
  color: #ffffff;
}

.solver-btn--back {
  background: var(--bg-primary);
  color: var(--text-primary);
  border: 1px solid var(--border);
}

.solver-btn--exit {
  background: var(--btn-function);
  color: var(--text-primary);
}

/* Root solver coefficients */
.root-coeffs {
  display: flex;
  flex-direction: column;
  gap: 6px;
  margin: 12px 0;
}

.root-coeff-row {
  display: flex;
  align-items: center;
  gap: 8px;
}

.root-coeff-label {
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 500;
  color: var(--accent);
  width: 40px;
  text-align: right;
}

.root-coeff-label sub {
  font-size: 0.7em;
}

.root-coeff-input {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 14px;
  padding: 8px 10px;
  flex: 1;
  outline: none;
}

.root-coeff-input:focus {
  border-color: var(--accent);
}

/* --- Palette: Logic / Base Conversion --- */
.base-inputs {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 16px;
}

.base-row {
  display: flex;
  align-items: center;
  gap: 8px;
}

.base-label {
  font-size: 12px;
  font-weight: 700;
  color: var(--accent);
  width: 36px;
  text-align: right;
}

.base-input {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 14px;
  padding: 8px 10px;
  flex: 1;
  min-width: 0;
  outline: none;
}

.base-input:focus {
  border-color: var(--accent);
}

.bit-grid {
  margin-top: 8px;
}

.bit-grid-label {
  font-size: 11px;
  color: var(--text-secondary);
  margin-bottom: 4px;
}

.bit-row {
  display: grid;
  grid-template-columns: repeat(16, 1fr);
  gap: 2px;
  margin-bottom: 6px;
}

.bit-btn {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: var(--bg-primary);
  color: var(--text-secondary);
  font-family: var(--font-display);
  font-size: 10px;
  padding: 4px 0;
  cursor: pointer;
  text-align: center;
  transition: all 0.1s;
  min-width: 0;
}

.bit-btn.active {
  background: var(--accent);
  color: #ffffff;
  border-color: var(--accent);
}

.base-clear-btn {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-ui);
  font-size: 13px;
  font-weight: 500;
  padding: 8px 16px;
  cursor: pointer;
  margin-top: 12px;
}

/* --- Palette: Fractions --- */
.frac-input-wrap {
  margin-bottom: 16px;
}

.frac-input {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 16px;
  padding: 10px 12px;
  width: 100%;
  outline: none;
}

.frac-input:focus {
  border-color: var(--accent);
}

.frac-results {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.frac-result {
  padding: 8px 12px;
  border-radius: 8px;
  font-family: var(--font-display);
  font-size: 15px;
  color: var(--text-primary);
  cursor: pointer;
}

.frac-result:nth-child(odd) {
  background: var(--bg-primary);
}

/* --- Palette: Help --- */
.help-content {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.6;
}

.help-content h3 {
  color: var(--text-primary);
  font-size: 15px;
  font-weight: 700;
  margin: 16px 0 6px;
}

.help-content h3:first-child {
  margin-top: 0;
}

/* --- iPhone-specific responsive --- */

/* iPhone SE / small screens */
@media (max-width: 374px) {
  :root {
    --gap: 4px;
    --font-size-display: 26px;
    --font-size-stack: 13px;
    --font-size-btn: 14px;
    --font-size-btn-small: 11px;
  }
  .btn { padding: 10px 0; min-height: 38px; }
  .btn--small { padding: 6px 0; min-height: 30px; }
  .btn--enter { padding: 12px 0; min-height: 44px; }
  .display { min-height: 115px; }
}

/* Standard iPhones (375-413px) */
@media (min-width: 375px) and (max-width: 413px) {
  :root {
    --gap: 6px;
    --font-size-display: 32px;
    --font-size-btn: 16px;
  }
}

/* Larger iPhones - Pro Max (414px+) */
@media (min-width: 414px) {
  :root {
    --gap: 7px;
    --font-size-display: 36px;
    --font-size-stack: 16px;
    --font-size-btn: 17px;
    --font-size-btn-small: 14px;
  }
  .btn { padding: 16px 0; }
  .btn--enter { padding: 18px 0; }
  .display { min-height: 150px; }
}

/* PWA standalone mode */
@media (display-mode: standalone) {
  .calculator {
    padding-top: var(--safe-top);
  }
}

/* Landscape prevention hint (calculator is portrait-only) */
@media (orientation: landscape) and (max-height: 500px) {
  .calculator::before {
    content: 'Please rotate to portrait mode';
    position: fixed;
    inset: 0;
    background: var(--bg-primary);
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 16px;
    font-weight: 500;
    z-index: 9999;
  }
}

/* --- Accent Color Themes --- */
.theme-green     { --accent: #2e7d32; --accent-hover: #1b5e20; }
.theme-blue      { --accent: #2196F3; --accent-hover: #1976D2; }
.theme-yellow    { --accent: #f57f17; --accent-hover: #e65100; }
.theme-pink      { --accent: #c2185b; --accent-hover: #ad1457; }
.theme-gray      { --accent: #546e7a; --accent-hover: #37474f; }
.theme-greenBlue { --accent: #2196F3; --accent-hover: #1976D2; }