:root {
  --blue: #3B82F6;
  --blue-dark: #2563EB;
  --blue-bg: #EFF6FF;
  --blue-border: #DBEAFE;
  --bg: #F3F4F6;
  --card: #FFFFFF;
  --text: #1F2937;
  --text-sub: #4B5563;
  --text-muted: #9CA3AF;
  --border: #E5E7EB;
  --warn-bg: #FFFBEB;
  --warn-text: #92400E;
  --error-bg: #FEF2F2;
  --error-border: #FECACA;
  --error-text: #B91C1C;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Apple SD Gothic Neo",
    "Noto Sans KR", "Malgun Gothic", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}

a {
  text-decoration: none;
  color: inherit;
}

/* Nav */
.nav {
  position: sticky;
  top: 0;
  z-index: 10;
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.nav-inner {
  max-width: 960px;
  margin: 0 auto;
  padding: 14px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand {
  display: flex;
  align-items: center;
  gap: 8px;
  font-weight: 800;
  font-size: 16px;
}

.brand-icon {
  width: 28px;
  height: 28px;
  border-radius: 8px;
}

.nav-links {
  display: flex;
  gap: 20px;
  font-size: 14px;
  font-weight: 600;
  color: var(--text-sub);
}

.nav-links a:hover {
  color: var(--blue);
}

/* Sections */
.section-inner {
  max-width: 960px;
  margin: 0 auto;
  padding: 64px 20px;
}

.section-inner.narrow {
  max-width: 560px;
}

.section-title {
  font-size: 24px;
  font-weight: 800;
  text-align: center;
  margin: 0 0 8px;
}

.section-sub {
  text-align: center;
  color: var(--text-sub);
  font-size: 15px;
  margin: 0 0 36px;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 13px 22px;
  border-radius: 12px;
  font-size: 15px;
  font-weight: 700;
  border: none;
  cursor: pointer;
  transition: transform 0.06s ease, opacity 0.15s ease;
}

.btn:active {
  transform: scale(0.97);
}

.btn-primary {
  background: var(--blue);
  color: #fff;
}

.btn-primary:hover {
  background: var(--blue-dark);
}

/* Calculator */
.calculator-section {
  background: #fff;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.calc-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 20px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
  margin-bottom: 20px;
}

.calc-title {
  font-size: 18px;
  font-weight: 700;
  margin: 0 0 16px;
}

.calc-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.calc-header .calc-title {
  margin: 0 0 16px;
}

.reset-btn {
  background: none;
  border: none;
  padding: 0;
  margin-bottom: 16px;
  font-size: 13px;
  font-family: inherit;
  color: var(--text-muted);
  cursor: pointer;
}

.reset-btn:hover {
  color: var(--text-sub);
  text-decoration: underline;
}

.input-group {
  margin-bottom: 16px;
}

.input-group label {
  display: block;
  font-size: 14px;
  font-weight: 500;
  color: var(--text-sub);
  margin-bottom: 8px;
}

.input-group input {
  width: 100%;
  background: #F9FAFB;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 16px;
  font-size: 16px;
  color: var(--text);
  font-family: inherit;
}

.input-group input:focus {
  outline: none;
  border-color: var(--blue);
}

.info-card,
.warning-card {
  border-radius: 16px;
  padding: 20px;
  text-align: center;
  font-size: 14px;
}

.info-card {
  background: var(--card);
  border: 1px solid var(--border);
  color: var(--text-muted);
}

.warning-card {
  background: var(--error-bg);
  border: 1px solid var(--error-border);
  color: var(--error-text);
  font-weight: 600;
}

.result-card {
  background: var(--card);
  border: 2px solid var(--blue);
  border-radius: 16px;
  padding: 20px;
  box-shadow: 0 4px 12px rgba(59, 130, 246, 0.1);
}

.result-card h3 {
  font-size: 20px;
  font-weight: 800;
  color: var(--blue);
  text-align: center;
  margin: 0 0 20px;
}

.result-box {
  padding: 16px;
  border-radius: 12px;
  border: 1px solid var(--border);
  margin-bottom: 12px;
}

.result-box.drinker {
  background: var(--blue-bg);
  border-color: var(--blue-border);
}

.result-box.non-drinker {
  background: #F9FAFB;
}

.result-box-label {
  font-size: 14px;
  color: var(--text-sub);
  font-weight: 500;
  margin: 0 0 4px;
}

.result-box-amount {
  font-size: 24px;
  font-weight: 800;
  margin: 0;
}

.result-box.drinker .result-box-amount {
  color: var(--blue);
}

.result-box.non-drinker .result-box-amount {
  color: var(--text);
}

.result-divider {
  border-top: 1px dashed var(--border);
  margin: 20px 0 16px;
}

.result-total-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
  font-size: 14px;
  color: var(--text-sub);
}

.result-total-row strong {
  font-size: 16px;
  color: var(--text);
}

.result-remainder {
  background: var(--warn-bg);
  color: var(--warn-text);
  border-radius: 8px;
  padding: 10px;
  font-size: 12px;
  text-align: center;
  margin-bottom: 16px;
}

.result-remainder p {
  margin: 4px 0;
}

.result-actions {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.result-copy-btn {
  background: var(--bg);
  color: var(--text-sub);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
}

.result-copy-btn:hover {
  background: #E5E7EB;
}

/* Footer */
.footer {
  text-align: center;
  padding: 32px 20px;
  color: var(--text-muted);
  font-size: 12px;
}

/* Responsive */
@media (max-width: 640px) {
  .nav-links {
    gap: 12px;
    font-size: 13px;
  }
}