html, body, main, header, footer {
  padding: 0px;
  margin: 0px;
}

:root {
  --md-primary: #6750A4;
  --md-on-primary: #FFFFFF;
  --md-primary-container: #EADDFF;
  --md-on-primary-container: #21005D;
  --md-secondary: #625B71;
  --md-secondary-container: #E8DEF8;
  --md-on-secondary-container: #1D192B;
  --md-tertiary: #7D5260;
  --md-tertiary-container: #FFD8E4;
  --md-surface: #FEF7FF;
  --md-surface-variant: #E7E0EC;
  --md-on-surface: #1C1B1F;
  --md-on-surface-variant: #49454F;
  --md-outline: #79747E;
  --md-outline-variant: #CAC4D0;
  --md-error: #B3261E;
  --md-error-container: #F9DEDC;
  --md-on-error: #FFFFFF;
  --md-shadow: rgba(0,0,0,0.1);
  --md-scrim: rgba(0,0,0,0.3);
  --ripple-color: rgba(103, 80, 164, 0.12);
}

body {
  font-family: 'Roboto', 'Noto Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  background: var(--md-surface);
  color: var(--md-on-surface);
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

header {
  width: 100%;
  display: flex;
  justify-content: center;
}

#ad-header {
  margin: 8px auto;
}

main {
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  flex: 1;
}

div#app {
  width: 100%;
  max-width: 400px;
  padding: 0 8px;
  box-sizing: border-box;
}

#calculator {
  background: var(--md-surface);
  border-radius: 24px;
  overflow: hidden;
  box-shadow: 0 1px 3px var(--md-shadow), 0 4px 12px var(--md-shadow);
  position: relative;
}

#display {
  background: var(--md-primary-container);
  padding: 24px 20px 16px;
  min-height: 100px;
  display: flex;
  flex-direction: column;
  position: relative;
  transition: background 0.3s;
}

#expression {
  font-size: 16px;
  color: var(--md-on-primary-container);
  opacity: 0.7;
  text-align: right;
  min-height: 24px;
  word-break: break-all;
  line-height: 1.4;
  transition: opacity 0.2s;
  font-family: 'Roboto Mono', 'Courier New', monospace;
}

#result {
  font-size: 40px;
  font-weight: 500;
  color: var(--md-on-primary-container);
  text-align: right;
  margin-top: 4px;
  word-break: break-all;
  line-height: 1.2;
  transition: font-size 0.15s;
  font-family: 'Roboto Mono', 'Courier New', monospace;
}

#result.small-text {
  font-size: 28px;
}

#result.xsmall-text {
  font-size: 20px;
}

#result.fade-in {
  animation: resultFadeIn 0.25s ease-out;
}

@keyframes resultFadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

#mode-indicator {
  position: absolute;
  top: 12px;
  left: 16px;
  font-size: 12px;
  font-weight: 600;
  color: var(--md-on-primary-container);
  opacity: 0.6;
  letter-spacing: 0.5px;
}

#error-msg {
  font-size: 13px;
  color: var(--md-error);
  text-align: right;
  min-height: 20px;
  margin-top: 2px;
  font-weight: 500;
  transition: opacity 0.2s;
}

#sci-toggle-bar {
  display: flex;
  align-items: center;
  padding: 8px 12px;
  gap: 6px;
  background: var(--md-surface);
  border-top: 1px solid var(--md-outline-variant);
}

#btn-sci-toggle {
  flex: 1;
  background: none;
  border: none;
  color: var(--md-primary);
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  padding: 8px 12px;
  border-radius: 8px;
  text-align: left;
  transition: background 0.2s;
}

#btn-sci-toggle:hover {
  background: var(--ripple-color);
}

#scientific-panel {
  background: var(--md-surface-variant);
  transition: max-height 0.3s ease, opacity 0.3s ease, padding 0.3s ease;
  overflow: hidden;
  max-height: 0;
  opacity: 0;
  padding: 0 8px;
}

#scientific-panel:not(.collapsed) {
  max-height: 420px;
  opacity: 1;
  padding: 8px;
  overflow-y: auto;
}

#scientific-panel.collapsed {
  max-height: 0;
  opacity: 0;
  padding: 0 8px;
}

.sci-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 6px;
  margin-bottom: 6px;
}

.sci-row:last-child {
  margin-bottom: 0;
}

.sci-btn {
  height: 44px;
  border: none;
  border-radius: 12px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  background: var(--md-surface);
  color: var(--md-on-surface);
  position: relative;
  overflow: hidden;
  transition: transform 0.1s, background 0.2s, box-shadow 0.2s;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2px;
  font-family: inherit;
  box-shadow: 0 1px 3px rgba(0,0,0,0.1), 0 1px 2px rgba(0,0,0,0.06);
  letter-spacing: 0.3px;
}

.sci-btn:hover {
  background: var(--md-primary-container);
  color: var(--md-on-primary-container);
  box-shadow: 0 2px 6px rgba(0,0,0,0.12);
}

.sci-btn:active {
  transform: scale(0.94);
  box-shadow: 0 1px 2px rgba(0,0,0,0.08);
}

.func-btn {
  background: var(--md-primary-container);
  color: var(--md-on-primary-container);
  box-shadow: 0 1px 3px rgba(103, 80, 164, 0.15);
}

.func-btn:hover {
  background: var(--md-primary);
  color: var(--md-on-primary);
  box-shadow: 0 3px 8px rgba(103, 80, 164, 0.25);
}

.sci-btn .btn-shortcut {
  position: absolute;
  top: 2px;
  left: 5px;
  font-size: 9px;
  opacity: 0.55;
  font-weight: 500;
  letter-spacing: 0;
}

.mode-btn {
  background: var(--md-tertiary-container);
  color: var(--md-on-secondary-container);
  font-weight: 700;
  letter-spacing: 1px;
}

.mode-btn:hover {
  background: var(--md-tertiary);
  color: var(--md-on-error);
}

.mode-btn.rad-mode {
  background: var(--md-primary);
  color: var(--md-on-primary);
}

.mode-btn.rad-mode:hover {
  background: var(--md-primary-container);
  color: var(--md-on-primary-container);
}

.toggle-btn {
  background: var(--md-outline-variant);
  color: var(--md-on-surface);
  font-weight: 700;
  letter-spacing: 0.5px;
}

.toggle-btn:hover {
  background: var(--md-outline);
  color: var(--md-on-error);
}

.toggle-btn.active {
  background: var(--md-primary);
  color: var(--md-on-primary);
  box-shadow: 0 2px 6px rgba(103, 80, 164, 0.3);
}

.toggle-btn.active:hover {
  background: var(--md-primary-container);
  color: var(--md-on-primary-container);
}

.second-func {
  display: none;
}

.show-second .second-func {
  display: flex;
}

.show-second .first-func.hidden-in-second {
  display: none;
}

.placeholder-btn {
  visibility: hidden;
}

#main-panel {
  padding: 8px;
  background: var(--md-surface);
}

.btn-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 6px;
  margin-bottom: 6px;
}

.btn-row:last-child {
  margin-bottom: 0;
}

.btn {
  height: 56px;
  border: none;
  border-radius: 16px;
  font-size: 20px;
  font-weight: 500;
  cursor: pointer;
  position: relative;
  overflow: hidden;
  transition: transform 0.1s, background 0.2s;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2px;
  font-family: inherit;
  min-height: 48px;
  touch-action: manipulation;
}

.btn:active {
  transform: scale(0.94);
}

.btn .btn-shortcut {
  position: absolute;
  top: 2px;
  left: 6px;
  font-size: 9px;
  opacity: 0.4;
  font-weight: 400;
}

.num-btn {
  background: var(--md-surface-variant);
  color: var(--md-on-surface);
}

.num-btn:hover {
  background: var(--md-outline-variant);
}

.operator-btn {
  background: var(--md-secondary-container);
  color: var(--md-on-secondary-container);
}

.operator-btn:hover {
  filter: brightness(0.95);
}

.action-btn {
  background: var(--md-error-container);
  color: var(--md-on-secondary-container);
  font-weight: 600;
}

.equals-btn {
  background: var(--md-primary);
  color: var(--md-on-primary);
  font-size: 24px;
  font-weight: 600;
}

.equals-btn:hover {
  filter: brightness(1.1);
}

.double-btn {
  grid-column: span 2;
}

.ripple {
  position: absolute;
  border-radius: 50%;
  background: var(--ripple-color);
  transform: scale(0);
  animation: rippleAnim 0.55s ease-out;
  pointer-events: none;
}

@keyframes rippleAnim {
  to {
    transform: scale(4);
    opacity: 0;
  }
}

.paren-unmatched {
  color: var(--md-error) !important;
  font-weight: 700;
}

#__fork {
  text-align: center;
  margin-top: 24px;
}

#__fork button {
  background: var(--md-primary);
  color: var(--md-on-primary);
  border: none;
  padding: 10px 24px;
  border-radius: 20px;
  font-size: 15px;
  cursor: pointer;
  font-weight: 500;
  transition: filter 0.2s;
}

#__fork button:hover {
  filter: brightness(1.1);
}

#features, #scenarios, #FAQ {
  max-width: 700px;
  width: 100%;
  padding: 24px 20px;
  box-sizing: border-box;
}

#features h2, #scenarios h2, #FAQ h2 {
  font-size: 22px;
  color: var(--md-primary);
  margin-bottom: 12px;
  font-weight: 600;
}

#features p {
  font-size: 15px;
  line-height: 1.7;
  color: var(--md-on-surface-variant);
  margin-bottom: 8px;
}

#scenarios ul {
  list-style: none;
  padding: 0;
}

#scenarios li {
  font-size: 15px;
  line-height: 1.7;
  color: var(--md-on-surface-variant);
  padding: 6px 0;
  border-bottom: 1px solid var(--md-outline-variant);
}

#scenarios li:last-child {
  border-bottom: none;
}

#scenarios li strong {
  color: var(--md-on-surface);
}

#FAQ dl {
  margin: 0;
}

#FAQ dt {
  font-size: 16px;
  font-weight: 600;
  color: var(--md-on-surface);
  margin-top: 16px;
  margin-bottom: 4px;
}

#FAQ dd {
  font-size: 15px;
  line-height: 1.7;
  color: var(--md-on-surface-variant);
  margin-left: 0;
  margin-bottom: 8px;
}

footer {
  width: 100%;
  text-align: center;
  padding: 20px;
  box-sizing: border-box;
}

@media (max-width: 420px) {
  div#app {
    padding: 0 4px;
  }

  #calculator {
    border-radius: 16px;
  }

  .btn {
    height: 50px;
    font-size: 18px;
    border-radius: 12px;
  }

  .sci-btn {
    height: 42px;
    font-size: 13px;
    border-radius: 10px;
    font-weight: 600;
  }

  #display {
    padding: 16px 14px 12px;
  }

  #result {
    font-size: 32px;
  }

  #expression {
    font-size: 14px;
  }

  #features, #scenarios, #FAQ {
    padding: 16px 12px;
  }
}