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

#app {
  max-width: 680px;
  margin: 20px auto;
  padding: 20px;
  background: #ffffff;
  border-radius: 16px;
  box-shadow: 0 2px 16px rgba(0, 0, 0, 0.08);
}

#app-title {
  text-align: center;
  font-size: 28px;
  font-weight: 700;
  color: #1a1a2e;
  margin: 0 0 24px 0;
  letter-spacing: 0.5px;
}

#converter {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

#mode-tabs {
  display: flex;
  border-radius: 10px;
  overflow: hidden;
  border: 2px solid #4A90D9;
}

.tab-btn {
  flex: 1;
  padding: 12px 16px;
  border: none;
  background: #ffffff;
  color: #4A90D9;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
}

.tab-btn.active {
  background: #4A90D9;
  color: #ffffff;
}

.tab-btn:hover:not(.active) {
  background: #e8f0fb;
}

#input-section {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

#input-label {
  font-size: 14px;
  font-weight: 600;
  color: #555;
}

#input-group {
  display: flex;
  align-items: center;
  border: 2px solid #ddd;
  border-radius: 10px;
  overflow: hidden;
  transition: border-color 0.2s ease;
}

#input-group:focus-within {
  border-color: #4A90D9;
}

#input-value {
  flex: 1;
  padding: 14px 16px;
  border: none;
  outline: none;
  font-size: 20px;
  color: #333;
  background: transparent;
}

#input-value::placeholder {
  color: #bbb;
  font-size: 15px;
}

#input-unit {
  padding: 14px 16px;
  font-size: 18px;
  font-weight: 600;
  color: #4A90D9;
  background: #f5f8fc;
  min-width: 48px;
  text-align: center;
}

#result-section {
  display: flex;
  justify-content: center;
}

#result-card {
  background: linear-gradient(135deg, #f0f5ff 0%, #e8f0fb 100%);
  border: 1px solid #d0dff5;
  border-radius: 12px;
  padding: 20px 28px;
  text-align: center;
  width: 100%;
}

#result-primary {
  display: flex;
  align-items: baseline;
  justify-content: center;
  gap: 8px;
  margin-bottom: 8px;
}

#result-value {
  font-size: 32px;
  font-weight: 700;
  color: #1a1a2e;
  word-break: break-all;
}

#result-unit {
  font-size: 18px;
  color: #4A90D9;
  font-weight: 600;
}

#result-expression {
  font-size: 14px;
  color: #666;
}

#result-exact {
  font-weight: 600;
  color: #333;
}

#preset-section {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

#preset-title {
  font-size: 15px;
  font-weight: 600;
  color: #555;
  margin: 0;
}

#preset-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}

.preset-btn {
  padding: 10px 6px;
  border: 1px solid #ddd;
  border-radius: 8px;
  background: #ffffff;
  color: #333;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.15s ease;
}

.preset-btn:hover {
  background: #4A90D9;
  color: #ffffff;
  border-color: #4A90D9;
}

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

#pi-reference {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 16px;
  background: #fafafa;
  border: 1px solid #eee;
  border-radius: 8px;
  font-size: 14px;
  color: #888;
}

#pi-value {
  font-weight: 600;
  color: #555;
  font-family: 'Courier New', monospace;
}

#__fork {
  text-align: center;
  margin: 16px 0;
}

#__fork button {
  padding: 10px 28px;
  border: none;
  border-radius: 8px;
  background: #4A90D9;
  color: #ffffff;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s ease;
}

#__fork button:hover {
  background: #357ABD;
}

#features, #scenarios, #FAQ {
  max-width: 680px;
  margin: 20px auto;
  padding: 0 20px;
}

#features h2, #scenarios h2, #FAQ h2 {
  font-size: 20px;
  color: #1a1a2e;
  margin: 0 0 12px 0;
}

#features p {
  font-size: 15px;
  line-height: 1.8;
  color: #555;
  margin: 0;
}

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

#scenarios li {
  font-size: 15px;
  line-height: 1.8;
  color: #555;
  margin-bottom: 6px;
}

#scenarios li strong {
  color: #333;
}

#FAQ dl {
  margin: 0;
}

#FAQ dt {
  font-size: 15px;
  font-weight: 600;
  color: #333;
  margin: 14px 0 4px 0;
}

#FAQ dd {
  font-size: 14px;
  line-height: 1.7;
  color: #666;
  margin: 0 0 8px 0;
  padding-left: 12px;
  border-left: 3px solid #e0e0e0;
}

@media (max-width: 768px) {
  #app {
    margin: 12px;
    padding: 16px;
    border-radius: 12px;
  }

  #app-title {
    font-size: 24px;
    margin-bottom: 18px;
  }

  #preset-grid {
    grid-template-columns: repeat(4, 1fr);
    gap: 6px;
  }

  .preset-btn {
    padding: 8px 4px;
    font-size: 13px;
  }

  #result-value {
    font-size: 26px;
  }

  #input-value {
    font-size: 18px;
    padding: 12px 14px;
  }
}

@media (max-width: 480px) {
  #preset-grid {
    grid-template-columns: repeat(3, 1fr);
    gap: 5px;
  }

  .preset-btn {
    padding: 8px 4px;
    font-size: 12px;
  }

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

  #result-value {
    font-size: 22px;
  }
}