:root {
  --color-primary: #2563eb;
  --color-primary-dark: #1d4ed8;
  --color-bg: #f4f6f8;
  --color-card: #e0ffff;
  --color-text: #1f2937;
  --color-muted: #6b7280;
  --color-border: #e2e8f0;
  --color-error-bg: #fef2f2;
  --color-error-border: #fecaca;
  --color-error-text: #b91c1c;
  --color-success-bg: #ecfdf5;
  --color-success-border: #a7f3d0;
  --color-success-text: #065f46;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.06);
}

* {
  box-sizing: border-box;
}

html, body {
  height: 100%;
}

body {
  margin: 0;
  font-family: "Segoe UI", system-ui, -apple-system, Roboto, Helvetica, Arial, sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  display: flex;
  flex-direction: column;
  min-height: 100%;
}

.container {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

/* ---------- Header ---------- */

.site-header {
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  color: #fff;
  box-shadow: var(--shadow);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
  padding: 1rem 1.5rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: #fff;
  text-decoration: none;
  font-size: 1.25rem;
  font-weight: 700;
}

.brand-icon {
  font-size: 1.4rem;
}

.main-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem;
}

.main-nav a {
  color: rgba(255, 255, 255, 0.85);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  padding: 0.5rem 0.75rem;
  border-radius: 999px;
  transition: background-color 0.15s ease, color 0.15s ease;
}

.main-nav a:hover {
  background: rgba(255, 255, 255, 0.15);
  color: #fff;
}

.main-nav a.active {
  background: rgba(255, 255, 255, 0.25);
  color: #fff;
}

/* ---------- Main content ---------- */

main.container {
  flex: 1;
  padding-top: 2.5rem;
  padding-bottom: 3rem;
}

h1 {
  margin: 0 0 0.5rem;
  font-size: 1.9rem;
}

.page-subtitle {
  color: var(--color-muted);
  margin-top: 0;
  margin-bottom: 1.5rem;
}

/* ---------- Hero / home page ---------- */

.hero {
  text-align: center;
  padding: 1rem 0 2.5rem;
}

.hero p {
  color: var(--color-muted);
  max-width: 560px;
  margin: 0.5rem auto 0;
}

.calc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 1.25rem;
}

.calc-card {
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.5rem;
  text-decoration: none;
  color: var(--color-text);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.calc-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.1);
}

.calc-icon {
  font-size: 1.75rem;
  display: block;
  margin-bottom: 0.5rem;
}

.calc-card h2 {
  margin: 0 0 0.4rem;
  font-size: 1.1rem;
}

.calc-card p {
  margin: 0;
  color: var(--color-muted);
  font-size: 0.9rem;
  line-height: 1.4;
}

/* ---------- Cards / forms ---------- */

.card {
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.75rem;
  max-width: 460px;
}

.form-group {
  margin-bottom: 1.1rem;
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.form-group label {
  font-weight: 600;
  font-size: 0.9rem;
}

.form-group input,
.form-group select,
.form-group textarea {
  padding: 0.55rem 0.7rem;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  font-size: 1rem;
  font-family: inherit;
  background: #fff;
  color: var(--color-text);
  resize: vertical;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.form-hint {
  margin: -0.5rem 0 1.1rem;
  color: var(--color-muted);
  font-size: 0.85rem;
}

.btn-primary {
  display: inline-block;
  background: var(--color-primary);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 0.65rem 1.4rem;
  font-size: 1rem;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 0.15s ease;
}

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

.btn-primary:disabled {
  background: var(--color-muted);
  cursor: not-allowed;
}

/* ---------- Antibiotic list ---------- */

.antibiotic-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.antibiotic-list li {
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 0.9rem 1.1rem;
}

.antibiotic-list a {
  color: var(--color-primary);
  text-decoration: none;
  font-weight: 600;
}

.antibiotic-list a:hover {
  text-decoration: underline;
}

/* ---------- Result / error boxes ---------- */

.result-box,
.error-box {
  margin-top: 1.25rem;
  padding: 0.9rem 1.1rem;
  border-radius: 8px;
  border: 1px solid;
  font-size: 0.95rem;
}

.result-box {
  background: var(--color-success-bg);
  border-color: var(--color-success-border);
  color: var(--color-success-text);
}

.error-box {
  background: var(--color-error-bg);
  border-color: var(--color-error-border);
  color: var(--color-error-text);
}

/* ---------- Footer ---------- */

.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 1.25rem 0;
  color: var(--color-muted);
  font-size: 0.85rem;
  text-align: center;
}

.site-footer p {
  margin: 0;
}

/* ---------- Responsive ---------- */

@media (max-width: 640px) {
  .header-inner {
    flex-direction: column;
    align-items: flex-start;
  }

  .card {
    max-width: 100%;
  }
}