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

:root {
  --md-primary: #6750A4;
  --md-on-primary: #FFFFFF;
  --md-primary-container: #EADDFF;
  --md-on-primary-container: #21005D;
  --md-surface: #FFFBFE;
  --md-surface-variant: #E7E0EC;
  --md-on-surface: #1C1B1F;
  --md-on-surface-variant: #49454F;
  --md-outline: #79747E;
  --md-error: #B3261E;
  --md-error-container: #F9DEDC;
  --md-on-error-container: #410E0B;
  --md-shadow: rgba(0, 0, 0, 0.08);
  --md-radius: 12px;
  --md-radius-btn: 28px;
}

* {
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  background: var(--md-surface);
  color: var(--md-on-surface);
  min-height: 100vh;
}

header {
  display: flex;
  justify-content: center;
  padding: 12px 16px 4px;
}

main {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 16px 24px;
}

footer {
  text-align: center;
  padding: 24px 16px 32px;
  color: var(--md-on-surface-variant);
  font-size: 14px;
}

footer a {
  color: var(--md-primary);
  text-decoration: none;
}

/* App Card */
#app {
  background: var(--md-surface);
  border-radius: 24px;
  padding: 32px 24px 28px;
  box-shadow: 0 2px 12px var(--md-shadow);
  border: 1px solid var(--md-surface-variant);
}

#app-title {
  text-align: center;
  font-size: 26px;
  font-weight: 700;
  color: var(--md-on-primary-container);
  margin: 0 0 6px;
  letter-spacing: -0.5px;
}

#app-desc {
  text-align: center;
  font-size: 14px;
  color: var(--md-on-surface-variant);
  margin: 0 0 28px;
}

/* Input Area */
#input-area {
  display: flex;
  align-items: flex-start;
  justify-content: center;
  gap: 16px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

.input-group {
  display: flex;
  flex-direction: column;
  flex: 1;
  min-width: 140px;
  max-width: 260px;
}

.input-group label {
  font-size: 13px;
  font-weight: 600;
  color: var(--md-on-surface-variant);
  margin-bottom: 6px;
  padding-left: 4px;
}

.input-group input {
  width: 100%;
  height: 48px;
  padding: 0 16px;
  font-size: 18px;
  font-family: inherit;
  border: 2px solid var(--md-outline);
  border-radius: 12px;
  background: var(--md-surface);
  color: var(--md-on-surface);
  outline: none;
  transition: border-color 0.2s, box-shadow 0.2s;
}

.input-group input:focus {
  border-color: var(--md-primary);
  box-shadow: 0 0 0 3px rgba(103, 80, 164, 0.15);
}

.input-group input.error {
  border-color: var(--md-error);
  box-shadow: 0 0 0 3px rgba(179, 38, 30, 0.12);
}

.error-msg {
  font-size: 12px;
  color: var(--md-error);
  margin-top: 4px;
  padding-left: 4px;
  min-height: 16px;
}

#op-indicator {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  min-width: 40px;
  height: 48px;
  margin-top: 22px;
  color: var(--md-primary);
  font-weight: 700;
}

/* Button Area */
#btn-area {
  margin-bottom: 24px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  align-items: center;
}

.btn-row {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
  width: 100%;
}

.btn-op {
  height: 48px;
  padding: 0 20px;
  font-size: 15px;
  font-weight: 600;
  font-family: inherit;
  border: none;
  border-radius: var(--md-radius-btn);
  cursor: pointer;
  transition: background 0.15s, box-shadow 0.15s, transform 0.1s;
  touch-action: manipulation;
  white-space: nowrap;
  min-width: 44px;
}

.btn-op:active {
  transform: scale(0.96);
}

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

.btn-binary:hover {
  background: #DFD0F8;
  box-shadow: 0 1px 4px var(--md-shadow);
}

.btn-binary.active {
  background: var(--md-primary);
  color: var(--md-on-primary);
  box-shadow: 0 2px 8px rgba(103, 80, 164, 0.3);
}

.btn-unary {
  background: #FFD8E4;
  color: #633B48;
}

.btn-unary:hover {
  background: #FFCAD9;
  box-shadow: 0 1px 4px var(--md-shadow);
}

.btn-unary.active {
  background: #D93B6B;
  color: #FFFFFF;
  box-shadow: 0 2px 8px rgba(217, 59, 107, 0.3);
}

/* Result Area */
#result-area {
  background: var(--md-primary-container);
  border-radius: 16px;
  padding: 20px 24px;
  display: none;
}

#result-area.visible {
  display: block;
}

#result-title {
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--md-on-primary-container);
  opacity: 0.7;
  margin-bottom: 8px;
}

#result-steps {
  font-size: 16px;
  color: var(--md-on-primary-container);
  line-height: 1.6;
  word-break: break-all;
}

#result-steps.single {
  font-size: 18px;
  font-weight: 600;
}

#result-final {
  font-size: 28px;
  font-weight: 700;
  color: var(--md-on-primary-container);
  margin-top: 12px;
  text-align: center;
  padding: 8px 0;
}

/* Fork button */
#__fork {
  text-align: right;
  margin-top: 16px;
}

#__fork button {
  height: 36px;
  padding: 0 18px;
  font-size: 13px;
  font-family: inherit;
  font-weight: 600;
  background: var(--md-primary);
  color: var(--md-on-primary);
  border: none;
  border-radius: 20px;
  cursor: pointer;
  transition: background 0.15s, box-shadow 0.15s;
  touch-action: manipulation;
}

#__fork button:hover {
  background: #5A4696;
  box-shadow: 0 2px 8px rgba(103, 80, 164, 0.35);
}

/* Extended Sections */
#features,
#scenarios,
#FAQ {
  margin-top: 32px;
  padding: 24px;
  background: var(--md-surface);
  border-radius: 20px;
  border: 1px solid var(--md-surface-variant);
}

#features h2,
#scenarios h2,
#FAQ h2 {
  font-size: 20px;
  font-weight: 700;
  color: var(--md-on-primary-container);
  margin: 0 0 12px;
}

#features p {
  font-size: 15px;
  color: var(--md-on-surface-variant);
  line-height: 1.7;
  margin: 0;
}

#scenarios ul {
  margin: 0;
  padding-left: 20px;
  list-style: disc;
}

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

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

#FAQ dl {
  margin: 0;
}

#FAQ dt {
  font-size: 15px;
  font-weight: 600;
  color: var(--md-on-surface);
  margin-top: 16px;
  margin-bottom: 4px;
}

#FAQ dt:first-child {
  margin-top: 0;
}

#FAQ dd {
  font-size: 14px;
  color: var(--md-on-surface-variant);
  line-height: 1.7;
  margin: 0 0 0 0;
  padding-left: 0;
}

/* Responsive */
@media (max-width: 480px) {
  #app {
    padding: 24px 16px 20px;
    border-radius: 20px;
  }

  #app-title {
    font-size: 22px;
  }

  #input-area {
    flex-direction: column;
    align-items: center;
    gap: 12px;
  }

  .input-group {
    width: 100%;
    max-width: 100%;
  }

  #op-indicator {
    margin-top: 0;
    height: 32px;
    font-size: 20px;
  }

  .btn-row {
    gap: 6px;
  }

  .btn-op {
    height: 44px;
    padding: 0 14px;
    font-size: 14px;
    border-radius: 22px;
  }

  #result-steps {
    font-size: 14px;
    word-break: break-all;
  }

  #result-final {
    font-size: 24px;
  }

  #features,
  #scenarios,
  #FAQ {
    padding: 20px 16px;
    border-radius: 16px;
  }
}