:root {
  --md-source: #6750A4;
  --md-primary: #6750A4;
  --md-on-primary: #FFFFFF;
  --md-primary-container: #EADDFF;
  --md-on-primary-container: #21005D;
  --md-secondary-container: #E8DEF8;
  --md-on-secondary-container: #1D192B;
  --md-tertiary-container: #FFD8E4;
  --md-on-tertiary-container: #31111D;
  --md-error: #B3261E;
  --md-error-container: #F9DEDC;
  --md-on-error-container: #410E0B;
  --md-surface: #FEF7FF;
  --md-surface-container: #FFFFFF;
  --md-surface-container-low: #F7F2FA;
  --md-surface-container-high: #ECE6F0;
  --md-on-surface: #1C1B1F;
  --md-on-surface-variant: #49454F;
  --md-outline: #79747E;
  --md-outline-variant: #CAC4D0;
  --md-elevation-1: 0 1px 2px rgba(0,0,0,0.3), 0 1px 3px 1px rgba(0,0,0,0.15);
  --md-elevation-2: 0 1px 2px rgba(0,0,0,0.3), 0 2px 6px 2px rgba(0,0,0,0.15);
  --md-elevation-3: 0 4px 8px 3px rgba(0,0,0,0.15), 0 1px 3px 0px rgba(0,0,0,0.3);
  --md-elevation-4: 0 6px 10px 4px rgba(0,0,0,0.15), 0 2px 3px 0px rgba(0,0,0,0.3);
  --md-shape-corner-xl: 28px;
  --md-shape-corner-l: 20px;
  --md-shape-corner-m: 16px;
  --md-shape-corner-s: 12px;
  --md-shape-corner-full: 999px;
  --md-typescale-display: 2.25rem;
  --md-typescale-headline: 1.5rem;
  --md-typescale-title: 1.25rem;
  --md-typescale-body: 1rem;
  --md-typescale-label: 0.875rem;
  --md-typescale-small: 0.75rem;
}

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

body {
  min-height: 100vh;
  background: #F0EBF4;
  background-image: radial-gradient(ellipse at 50% 0%, rgba(103,80,164,0.08) 0%, transparent 60%);
  background-attachment: fixed;
  font-family: "Google Sans Text", "Google Sans", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  color: var(--md-on-surface);
}

#app {
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 16px;
  box-sizing: border-box;
}

#calculator {
  width: 100%;
  max-width: 360px;
  background: var(--md-surface-container);
  border-radius: var(--md-shape-corner-xl);
  box-shadow: var(--md-elevation-3);
  overflow: hidden;
  touch-action: manipulation;
}

#display-container {
  padding: 20px 20px 16px;
  background: var(--md-surface-container);
  border-bottom: 1px solid var(--md-outline-variant);
  display: flex;
  flex-direction: column;
  gap: 6px;
}

#formula {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-label);
  font-weight: 400;
  color: var(--md-on-surface-variant);
  text-align: right;
  min-height: 1.25rem;
  line-height: 1.25rem;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  padding: 0 4px;
  letter-spacing: 0.014em;
}

#display {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-display);
  font-weight: 500;
  color: var(--md-on-surface);
  text-align: right;
  min-height: 3rem;
  line-height: 3rem;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  padding: 8px 12px;
  border-radius: var(--md-shape-corner-s);
  background: var(--md-surface-container-low);
  border: 2px solid transparent;
  transition: border-color 0.2s cubic-bezier(0.4,0,0.2,1), font-size 0.15s cubic-bezier(0.4,0,0.2,1), background-color 0.2s cubic-bezier(0.4,0,0.2,1);
  letter-spacing: 0.006em;
}

#display.error {
  color: var(--md-error);
  border-color: var(--md-error);
  background: var(--md-error-container);
  animation: flash-border 0.5s cubic-bezier(0.4,0,0.2,1);
}

#display.shake {
  animation: shake 0.3s cubic-bezier(0.4,0,0.2,1);
}

#keypad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  padding: 12px 16px 16px;
  background: var(--md-surface-container);
}

.btn {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 52px;
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-title);
  font-weight: 500;
  border: none;
  border-radius: var(--md-shape-corner-full);
  cursor: pointer;
  background: var(--md-surface-container-low);
  color: var(--md-on-surface);
  transition: background 0.15s cubic-bezier(0.4,0,0.2,1), transform 0.15s cubic-bezier(0.4,0,0.2,1), box-shadow 0.15s cubic-bezier(0.4,0,0.2,1);
  touch-action: manipulation;
  outline: none;
  user-select: none;
  -webkit-user-select: none;
  box-shadow: var(--md-elevation-1);
  position: relative;
  overflow: hidden;
  letter-spacing: 0.009em;
}

.btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: transparent;
  transition: background 0.15s cubic-bezier(0.4,0,0.2,1);
  border-radius: inherit;
  pointer-events: none;
}

.btn:hover::after {
  background: rgba(103, 80, 164, 0.08);
}

.btn:active {
  transform: scale(0.95);
  box-shadow: none;
}

.btn:active::after {
  background: rgba(103, 80, 164, 0.12);
}

.btn-number {
  background: var(--md-surface-container-high);
  color: var(--md-on-surface);
}

.btn-number:hover::after {
  background: rgba(103, 80, 164, 0.08);
}

.btn-number:active {
  background: var(--md-surface-container-high);
}

.btn-number:active::after {
  background: rgba(103, 80, 164, 0.12);
}

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

.btn-operator:hover::after {
  background: rgba(29, 25, 43, 0.08);
}

.btn-operator:active::after {
  background: rgba(29, 25, 43, 0.12);
}

#btn-clear {
  background: var(--md-error-container);
  color: var(--md-on-error-container);
  font-weight: 600;
}

#btn-clear:hover::after {
  background: rgba(179, 38, 30, 0.08);
}

#btn-clear:active::after {
  background: rgba(179, 38, 30, 0.12);
}

#btn-equals {
  background: var(--md-primary);
  color: var(--md-on-primary);
  font-weight: 700;
  box-shadow: var(--md-elevation-2);
}

#btn-equals:hover::after {
  background: rgba(255, 255, 255, 0.08);
}

#btn-equals:active {
  box-shadow: var(--md-elevation-1);
}

#btn-equals:active::after {
  background: rgba(255, 255, 255, 0.12);
}

.btn-span-2 {
  grid-column: span 2;
  border-radius: var(--md-shape-corner-full);
}

@media (max-width: 480px) {
  #calculator {
    max-width: 100%;
    border-radius: var(--md-shape-corner-l);
  }
  .btn {
    min-height: 60px;
    font-size: 1.35rem;
  }
  #display {
    font-size: 2.5rem;
    line-height: 3.5rem;
    min-height: 3.5rem;
  }
  #display-container {
    padding: 24px 20px 20px;
  }
  #formula {
    font-size: 0.9rem;
    min-height: 1.4rem;
    line-height: 1.4rem;
  }
  #keypad {
    gap: 10px;
    padding: 14px 18px 18px;
  }
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  10%, 50%, 90% { transform: translateX(-4px); }
  30%, 70% { transform: translateX(4px); }
}

#__fork {
  text-align: center;
  padding: 24px 16px 32px;
}

#__fork button {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-body);
  font-weight: 500;
  color: var(--md-primary);
  background: var(--md-primary-container);
  border: none;
  border-radius: var(--md-shape-corner-full);
  padding: 10px 32px;
  cursor: pointer;
  transition: background 0.15s cubic-bezier(0.4,0,0.2,1), transform 0.15s cubic-bezier(0.4,0,0.2,1), box-shadow 0.15s cubic-bezier(0.4,0,0.2,1);
  box-shadow: var(--md-elevation-1);
  touch-action: manipulation;
  outline: none;
}

#__fork button:hover {
  background: rgba(103, 80, 164, 0.2);
  box-shadow: var(--md-elevation-2);
}

#__fork button:active {
  transform: scale(0.95);
  box-shadow: none;
}

#features, #scenarios, #FAQ {
  max-width: 720px;
  margin: 0 auto;
  padding: 40px 20px;
}

#features h2, #scenarios h2, #FAQ h2 {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-headline);
  font-weight: 500;
  color: var(--md-on-surface);
  text-align: center;
  margin: 0 0 28px 0;
}

#features .section-content {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 16px;
}

.feature-card {
  background: var(--md-surface-container);
  border-radius: var(--md-shape-corner-l);
  padding: 20px;
  box-shadow: var(--md-elevation-1);
  transition: box-shadow 0.2s cubic-bezier(0.4,0,0.2,1);
}

.feature-card:hover {
  box-shadow: var(--md-elevation-2);
}

.feature-icon {
  font-size: 2rem;
  display: block;
  margin-bottom: 10px;
}

.feature-card h3 {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-title);
  font-weight: 500;
  color: var(--md-on-surface);
  margin: 0 0 6px 0;
}

.feature-card p {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-label);
  color: var(--md-on-surface-variant);
  line-height: 1.5;
  margin: 0;
}

#scenarios .section-content {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.scenario-item {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  background: var(--md-surface-container);
  border-radius: var(--md-shape-corner-l);
  padding: 18px 20px;
  box-shadow: var(--md-elevation-1);
  transition: box-shadow 0.2s cubic-bezier(0.4,0,0.2,1);
}

.scenario-item:hover {
  box-shadow: var(--md-elevation-2);
}

.scenario-icon {
  font-size: 1.75rem;
  flex-shrink: 0;
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--md-surface-container-low);
  border-radius: var(--md-shape-corner-s);
}

.scenario-item h3 {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-title);
  font-weight: 500;
  color: var(--md-on-surface);
  margin: 0 0 4px 0;
}

.scenario-item p {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-label);
  color: var(--md-on-surface-variant);
  line-height: 1.5;
  margin: 0;
}

#FAQ .section-content {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.faq-item {
  background: var(--md-surface-container);
  border-radius: var(--md-shape-corner-l);
  box-shadow: var(--md-elevation-1);
  overflow: hidden;
}

.faq-item summary {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-body);
  font-weight: 500;
  color: var(--md-on-surface);
  padding: 16px 20px;
  cursor: pointer;
  outline: none;
  list-style: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
  transition: background 0.15s cubic-bezier(0.4,0,0.2,1);
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::after {
  content: '▸';
  font-size: 0.875rem;
  color: var(--md-on-surface-variant);
  transition: transform 0.2s cubic-bezier(0.4,0,0.2,1);
}

.faq-item[open] summary::after {
  transform: rotate(90deg);
}

.faq-item summary:hover {
  background: var(--md-surface-container-low);
}

.faq-item p {
  font-family: "Google Sans Text", Roboto, system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: var(--md-typescale-label);
  color: var(--md-on-surface-variant);
  line-height: 1.6;
  margin: 0;
  padding: 0 20px 18px 20px;
}

@media (max-width: 480px) {
  #features .section-content {
    grid-template-columns: 1fr;
  }
  #features, #scenarios, #FAQ {
    padding: 32px 16px;
  }
  #features h2, #scenarios h2, #FAQ h2 {
    font-size: 1.35rem;
    margin-bottom: 20px;
  }
}

@keyframes flash-border {
  0% { border-color: var(--md-error); }
  100% { border-color: transparent; }
}