*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg: #0f0f14;
  --surface: #1a1a24;
  --surface-raised: #22222f;
  --border: #2e2e40;
  --text: #e8e8f0;
  --text-muted: #8888aa;
  --yellow: #f0c040;
  --yellow-dim: #c09828;
  --purple: #9060d8;
  --purple-bright: #b080f8;
  --purple-dim: #5a3a9a;
  --radius: 8px;
}

body {
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: grid;
  grid-template-columns: 220px 1fr;
  grid-template-rows: auto 1fr auto;
  grid-template-areas:
    "header header"
    "nav    main"
    "footer footer";
}

/* ── Header ── */
header {
  grid-area: header;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 1rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 1rem;
}

header .logo {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--yellow);
  letter-spacing: -0.5px;
  text-decoration: none;
}

header .logo span {
  color: var(--purple-bright);
}

/* ── Sidebar nav ── */
nav {
  grid-area: nav;
  background: var(--surface);
  border-right: 1px solid var(--border);
  padding: 1.5rem 0;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

nav .nav-section {
  padding: 0.25rem 1rem 0.5rem;
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
}

nav a {
  display: block;
  padding: 0.55rem 1rem;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  border-left: 3px solid transparent;
  transition: color 0.15s, border-color 0.15s, background 0.15s;
}

nav a:hover {
  color: var(--text);
  background: var(--surface-raised);
}

nav a.active {
  color: var(--yellow);
  border-left-color: var(--yellow);
  background: var(--surface-raised);
}

/* ── Main content ── */
main {
  grid-area: main;
  padding: 2rem 2.5rem;
  max-width: 780px;
}

h1 {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--yellow);
  margin-bottom: 0.5rem;
}

h2 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--purple-bright);
  margin-bottom: 1rem;
  margin-top: 2rem;
}

p {
  line-height: 1.65;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

/* ── Cards (used on index) ── */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 1rem;
  margin-top: 1.5rem;
}

.card {
  background: var(--surface-raised);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1rem;
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.2s, transform 0.15s;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.card:hover {
  border-color: var(--purple);
  transform: translateY(-2px);
}

.card .card-title {
  font-weight: 600;
  color: var(--yellow);
  font-size: 0.95rem;
}

.card .card-desc {
  font-size: 0.82rem;
  color: var(--text-muted);
  line-height: 1.5;
}

/* ── Calculator widgets ── */
.calc-card {
  background: var(--surface-raised);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.75rem;
  margin-top: 1.5rem;
}

.field-group {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  margin-bottom: 1.25rem;
}

label {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

input[type="date"],
input[type="number"],
select {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text);
  font-size: 1rem;
  padding: 0.55rem 0.75rem;
  width: 100%;
  outline: none;
  transition: border-color 0.15s;
}

input[type="date"]:focus,
input[type="number"]:focus,
select:focus {
  border-color: var(--purple);
}

input[type="date"]::-webkit-calendar-picker-indicator {
  filter: invert(0.7);
  cursor: pointer;
}

.row {
  display: flex;
  gap: 0.75rem;
  align-items: flex-end;
}

.row .field-group {
  flex: 1;
}

.row .field-group.narrow {
  flex: 0 0 90px;
}

/* ── Toggle pill ── */
.toggle-group {
  display: flex;
  gap: 0;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}

.toggle-group input[type="radio"] {
  display: none;
}

.toggle-group label {
  flex: 1;
  text-align: center;
  padding: 0.55rem 1rem;
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: none;
  letter-spacing: 0;
  background: transparent;
  border: none;
  transition: background 0.15s, color 0.15s;
  user-select: none;
}

.toggle-group input[type="radio"]:checked + label {
  background: var(--purple-dim);
  color: var(--text);
}

/* ── Button ── */
button.calc-btn {
  background: var(--yellow);
  color: #1a1400;
  border: none;
  border-radius: var(--radius);
  padding: 0.65rem 1.5rem;
  font-size: 0.95rem;
  font-weight: 700;
  cursor: pointer;
  transition: background 0.15s, transform 0.1s;
  margin-top: 0.25rem;
}

button.calc-btn:hover {
  background: var(--yellow-dim);
}

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

/* ── Result box ── */
.result {
  margin-top: 1.5rem;
  background: var(--surface);
  border: 1px solid var(--purple-dim);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  display: none;
}

.result.visible {
  display: block;
}

.result-label {
  font-size: 0.78rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-muted);
  margin-bottom: 0.35rem;
}

.result-date {
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--yellow);
}

.result-detail {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: 0.4rem;
}

/* ── Footer ── */
footer {
  grid-area: footer;
  background: var(--surface);
  border-top: 1px solid var(--border);
  padding: 0.75rem 1.5rem;
  font-size: 0.78rem;
  color: var(--text-muted);
}

/* ── Hamburger button (hidden on desktop) ── */
.hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  margin-left: auto;
  background: none;
  border: none;
  cursor: pointer;
  padding: 4px 6px;
}

.hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text);
  border-radius: 2px;
  transition: transform 0.2s ease, opacity 0.2s ease;
}

.hamburger.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.hamburger.open span:nth-child(2) { opacity: 0; }
.hamburger.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ── Responsive ── */
@media (max-width: 640px) {
  body {
    grid-template-columns: 1fr;
    grid-template-rows: auto auto 1fr auto;
    grid-template-areas:
      "header"
      "nav"
      "main"
      "footer";
  }

  .hamburger {
    display: flex;
  }

  nav {
    border-right: none;
    border-bottom: 1px solid var(--border);
    flex-direction: column;
    padding: 0;
    gap: 0;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.25s ease;
  }

  nav.open {
    max-height: 400px;
    padding: 0.5rem 0;
  }

  nav a {
    border-left: 3px solid transparent;
  }

  main {
    padding: 1.25rem 1rem;
  }
}