/* Base reset & typography */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --nav-height: 64px;
  --radius-xl: 24px;
  --radius-lg: 18px;
  --radius-pill: 999px;
}

/* THEME VARIABLES */
body.dark-theme {
  --bg: radial-gradient(circle at top, #020617 0, #020617 30%, #020617 55%, #020617 100%);
  --bg-solid: #020617;
  --bg-elevated: #020617;
  --bg-card: rgba(15, 23, 42, 0.95);
  --bg-screen: #020617;
  --text: #e5e7eb;
  --muted: #9ca3af;
  --border-soft: rgba(148, 163, 184, 0.4);
  --accent: #22d3ee;
  --accent-soft: rgba(34, 211, 238, 0.25);
  --accent-strong: rgba(45, 212, 191, 0.6);
  --danger: #fb7185;
}

body.light-theme {
  --bg: radial-gradient(circle at top, #e5f0ff 0, #f9fafb 40%, #f3f4f6 100%);
  --bg-solid: #f3f4f6;
  --bg-elevated: #ffffff;
  --bg-card: #ffffff;
  --bg-screen: #f9fafb;
  --text: #111827;
  --muted: #6b7280;
  --border-soft: rgba(209, 213, 219, 0.9);
  --accent: #2563eb;
  --accent-soft: rgba(37, 99, 235, 0.15);
  --accent-strong: rgba(59, 130, 246, 0.5);
  --danger: #b91c1c;
}

body {
  min-height: 100vh;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Poppins", sans-serif;
  background: var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
}

/* NAVBAR */
.navbar {
  position: fixed;
  inset-inline: 0;
  top: 0;
  height: var(--nav-height);
  padding-inline: 1.2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: linear-gradient(
    to bottom,
    rgba(15, 23, 42, 0.95),
    rgba(15, 23, 42, 0.7),
    transparent
  );
  backdrop-filter: blur(18px);
  border-bottom: 1px solid var(--border-soft);
  z-index: 50;
}

body.light-theme .navbar {
  background: linear-gradient(
    to bottom,
    rgba(249, 250, 251, 0.98),
    rgba(249, 250, 251, 0.85),
    transparent
  );
}

/* Brand */
.brand {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  font-size: 0.9rem;
}

.brand-dot {
  width: 12px;
  height: 12px;
  border-radius: 999px;
  background: radial-gradient(circle, #22d3ee, #0ea5e9, transparent 70%);
  box-shadow:
    0 0 12px rgba(56, 189, 248, 0.9),
    0 0 24px rgba(45, 212, 191, 0.6);
}

.brand-text span {
  color: var(--accent);
}

/* Nav links */
.nav-links {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
  justify-content: center;
}

.nav-link {
  border: 1px solid transparent;
  padding: 0.35rem 0.85rem;
  border-radius: var(--radius-pill);
  background: transparent;
  cursor: pointer;
  font-size: 0.83rem;
  color: var(--muted);
  transition:
    color 0.2s ease,
    background 0.2s ease,
    border-color 0.2s ease,
    transform 0.1s ease;
}

.nav-link:hover {
  color: var(--text);
  border-color: var(--accent-soft);
  background: rgba(15, 23, 42, 0.6);
  transform: translateY(-1px);
}

body.light-theme .nav-link:hover {
  background: rgba(243, 244, 246, 0.95);
}

.nav-link.active {
  color: #0f172a;
  background: linear-gradient(135deg, #22d3ee, #4ade80);
  border-color: transparent;
  box-shadow:
    0 0 18px var(--accent-strong),
    0 0 40px rgba(34, 211, 238, 0.45);
  transform: translateY(-1px);
}

/* Theme toggle */
.theme-toggle {
  border-radius: 999px;
  border: 1px solid var(--border-soft);
  background: radial-gradient(circle at 10% 0, var(--accent-soft), transparent 60%);
  width: 40px;
  height: 40px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: 1.1rem;
  color: var(--text);
  box-shadow:
    0 0 0 1px rgba(15, 23, 42, 0.6),
    0 0 18px var(--accent-strong);
  transition:
    transform 0.1s ease,
    box-shadow 0.2s ease,
    background 0.2s ease;
}

.theme-toggle:hover {
  transform: translateY(-1px);
  box-shadow:
    0 0 0 1px rgba(148, 163, 184, 0.8),
    0 0 22px var(--accent-strong);
}

.theme-toggle .icon {
  pointer-events: none;
}

/* MAIN & SECTIONS */
.main {
  position: relative;
  max-width: 1024px;
  margin: 0 auto;
  padding: calc(var(--nav-height) + 1.5rem) 1.2rem 2rem;
  min-height: calc(100vh - var(--nav-height));
}

/* Sections act like SPA pages */
.section {
  position: absolute;
  inset: calc(var(--nav-height) + 0.5rem) 1.2rem 1.5rem;
  max-width: 1024px;
  margin: 0 auto;
  opacity: 0;
  transform: translateY(20px) scale(0.99);
  filter: blur(4px);
  pointer-events: none;
  transition:
    opacity 0.35s ease,
    transform 0.35s ease,
    filter 0.35s ease;
}

.section.active {
  opacity: 1;
  transform: translateY(0) scale(1);
  filter: blur(0);
  pointer-events: auto;
}

/* On small screens, allow scroll */
@media (max-width: 768px) {
  .section {
    inset: calc(var(--nav-height) + 0.7rem) 0.75rem 1rem;
  }
}

/* HOME SECTION */
.home-content {
  max-width: 720px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
  border-radius: var(--radius-xl);
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.16), transparent 55%),
    radial-gradient(circle at 100% 0, rgba(94, 234, 212, 0.14), transparent 55%),
    linear-gradient(135deg, rgba(15, 23, 42, 0.96), rgba(15, 23, 42, 0.9));
  border: 1px solid rgba(148, 163, 184, 0.4);
  box-shadow:
    0 0 0 1px rgba(15, 23, 42, 0.9),
    0 0 24px rgba(34, 211, 238, 0.45),
    0 0 48px rgba(45, 212, 191, 0.4);
}

body.light-theme .home-content {
  background: linear-gradient(135deg, #ffffff, #eff6ff);
  box-shadow:
    0 10px 26px rgba(15, 23, 42, 0.14),
    0 0 0 1px rgba(209, 213, 219, 0.9);
}

.home-content h1 {
  font-size: clamp(2rem, 3vw, 2.5rem);
  margin-bottom: 0.75rem;
}

.home-content h1 span {
  background: linear-gradient(135deg, #22d3ee, #4ade80);
  -webkit-background-clip: text;
  color: transparent;
}

.home-content p {
  color: var(--muted);
  margin-bottom: 1.25rem;
}

/* Home buttons */
.home-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.pill-button {
  border-radius: var(--radius-pill);
  padding: 0.55rem 1.25rem;
  font-size: 0.9rem;
  border: 1px solid transparent;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.35rem;
  transition:
    background 0.2s ease,
    transform 0.1s ease,
    box-shadow 0.2s ease,
    color 0.2s ease;
}

.pill-button.primary {
  background: linear-gradient(135deg, #22d3ee, #4ade80);
  color: #0f172a;
  box-shadow:
    0 0 18px rgba(34, 211, 238, 0.7),
    0 0 36px rgba(45, 212, 191, 0.7);
}

.pill-button.primary:hover {
  transform: translateY(-1px);
}

.pill-button.ghost {
  background: transparent;
  border-color: var(--border-soft);
  color: var(--text);
}

.pill-button.ghost:hover {
  background: rgba(15, 23, 42, 0.8);
}

body.light-theme .pill-button.ghost:hover {
  background: rgba(243, 244, 246, 0.96);
}

.pill-button.full-width {
  width: 100%;
}

/* Home feature cards */
.home-grid {
  display: grid;
  gap: 0.75rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

@media (max-width: 768px) {
  .home-grid {
    grid-template-columns: 1fr;
  }
}

.home-card {
  border-radius: 18px;
  padding: 0.9rem 1rem;
  border: 1px solid rgba(148, 163, 184, 0.5);
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.16), transparent 55%),
    rgba(15, 23, 42, 0.9);
  font-size: 0.9rem;
}

body.light-theme .home-card {
  background: #ffffff;
}

/* CALCULATOR LAYOUT */
.calc-layout {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
}

.calc-card {
  width: 100%;
  max-width: 360px;
  padding: 1.2rem;
  border-radius: 28px;
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.16), transparent 55%),
    radial-gradient(circle at 100% 0, rgba(59, 130, 246, 0.14), transparent 55%),
    linear-gradient(145deg, rgba(15, 23, 42, 0.98), rgba(15, 23, 42, 0.95));
  border: 1px solid rgba(148, 163, 184, 0.55);
  box-shadow:
    0 0 0 1px rgba(15, 23, 42, 0.9),
    0 0 26px rgba(34, 211, 238, 0.55),
    0 0 52px rgba(45, 212, 191, 0.45);
}

.calc-card.tall {
  max-width: 420px;
}

body.light-theme .calc-card {
  background: linear-gradient(145deg, #ffffff, #eff6ff);
  box-shadow:
    0 12px 28px rgba(15, 23, 42, 0.16),
    0 0 0 1px rgba(209, 213, 219, 0.95);
}

/* Calculator header */
.calc-header {
  margin-bottom: 0.85rem;
}

.calc-header h2 {
  font-size: 1.2rem;
  margin-bottom: 0.15rem;
}

.calc-header p {
  font-size: 0.8rem;
  color: var(--muted);
}

/* Display */
.calc-screen {
  margin-bottom: 1rem;
  border-radius: 18px;
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.12), transparent 55%),
    var(--bg-screen);
  border: 1px solid rgba(148, 163, 184, 0.5);
  padding: 0.65rem 0.85rem;
  box-shadow:
    inset 0 0 12px rgba(15, 23, 42, 0.9),
    0 0 24px rgba(34, 211, 238, 0.35);
}

.calc-screen input {
  width: 100%;
  border: none;
  outline: none;
  background: transparent;
  color: var(--text);
  font-size: 1.8rem;
  text-align: right;
  font-weight: 500;
  overflow-x: auto;
  white-space: nowrap;
}

/* KEYS GRID */
.calc-keys {
  display: grid;
  gap: 0.6rem;
}

.simple-keys {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.scientific-keys {
  grid-template-columns: repeat(5, minmax(0, 1fr));
}

/* Buttons */
.btn {
  border: none;
  border-radius: 18px;
  padding: 0.7rem 0.2rem;
  cursor: pointer;
  font-size: 0.98rem;
  font-weight: 500;
  color: var(--text);
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.12), transparent 55%),
    rgba(15, 23, 42, 0.95);
  box-shadow:
    0 0 0 1px rgba(15, 23, 42, 0.9),
    -3px -3px 9px rgba(15, 23, 42, 0.9),
    0 0 18px rgba(34, 211, 238, 0.25);
  transition:
    transform 0.08s ease,
    box-shadow 0.12s ease,
    background 0.12s ease;
}

body.light-theme .btn {
  background: #f3f4f6;
  box-shadow:
    0 1px 3px rgba(15, 23, 42, 0.18),
    0 0 0 1px rgba(209, 213, 219, 0.95);
}

.btn:active {
  transform: translateY(1px) scale(0.99);
  box-shadow:
    0 0 0 1px rgba(15, 23, 42, 0.9),
    0 0 8px rgba(34, 211, 238, 0.35);
}

.btn-operator {
  color: #22d3ee;
}

body.light-theme .btn-operator {
  color: #2563eb;
}

.btn-ac {
  color: var(--danger);
}

.btn-equal {
  background: linear-gradient(135deg, #22d3ee, #4ade80);
  color: #0f172a;
  box-shadow:
    0 0 18px rgba(34, 211, 238, 0.75),
    0 0 36px rgba(45, 212, 191, 0.7);
}

.btn-equal:active {
  transform: translateY(1px) scale(0.99);
}

.span-2 {
  grid-column: span 2;
}

/* AGE CALCULATOR */
.age-layout {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
}

.age-card {
  width: 100%;
  max-width: 420px;
  padding: 1.3rem 1.35rem 1.5rem;
  border-radius: 28px;
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.16), transparent 55%),
    linear-gradient(145deg, rgba(15, 23, 42, 0.99), rgba(15, 23, 42, 0.95));
  border: 1px solid rgba(148, 163, 184, 0.55);
  box-shadow:
    0 0 0 1px rgba(15, 23, 42, 0.9),
    0 0 26px rgba(34, 211, 238, 0.55),
    0 0 52px rgba(45, 212, 191, 0.45);
}

body.light-theme .age-card {
  background: linear-gradient(145deg, #ffffff, #eff6ff);
  box-shadow:
    0 12px 28px rgba(15, 23, 42, 0.16),
    0 0 0 1px rgba(209, 213, 219, 0.95);
}

/* Age form */
.age-form {
  margin-top: 1rem;
  margin-bottom: 1.1rem;
}

.age-form label {
  display: block;
  font-size: 0.9rem;
  margin-bottom: 0.35rem;
}

.age-form input[type="date"] {
  width: 100%;
  border-radius: 14px;
  border: 1px solid rgba(148, 163, 184, 0.7);
  padding: 0.55rem 0.75rem;
  background: rgba(15, 23, 42, 0.9);
  color: var(--text);
  font-size: 0.9rem;
  margin-bottom: 0.7rem;
}

body.light-theme .age-form input[type="date"] {
  background: #f9fafb;
}

.age-form input[type="date"]:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 1px var(--accent-soft);
}

/* Age result */
.age-result {
  display: flex;
  gap: 0.75rem;
  justify-content: space-between;
  flex-wrap: wrap;
}

.age-pill {
  flex: 1;
  min-width: 90px;
  border-radius: 20px;
  padding: 0.65rem 0.5rem;
  background: radial-gradient(circle at 0 0, rgba(34, 211, 238, 0.12), transparent 55%),
    rgba(15, 23, 42, 0.96);
  border: 1px solid rgba(148, 163, 184, 0.7);
  text-align: center;
  box-shadow:
    0 0 16px rgba(34, 211, 238, 0.4),
    0 0 32px rgba(45, 212, 191, 0.35);
}

body.light-theme .age-pill {
  background: #f9fafb;
  box-shadow:
    0 6px 16px rgba(15, 23, 42, 0.12),
    0 0 0 1px rgba(209, 213, 219, 0.9);
}

.age-pill span:first-child {
  display: block;
  font-size: 1.4rem;
  font-weight: 600;
}

.age-pill span:last-child {
  font-size: 0.8rem;
  color: var(--muted);
}

.error-text {
  margin-top: 0.3rem;
  font-size: 0.8rem;
  color: var(--danger);
}

/* RESPONSIVE */
@media (max-width: 640px) {
  .navbar {
    padding-inline: 0.85rem;
  }

  .main {
    padding-inline: 0.75rem;
  }

  .calc-card,
  .age-card,
  .home-content {
    padding: 1.1rem 1rem;
  }

  .calc-screen input {
    font-size: 1.6rem;
  }
}