:root {
  --bg: #0b0e14;
  --fg: #e6e9ef;
  --muted: #9aa4b2;
  --accent: #f6821f;
  --card: #141924;
  --border: #232a38;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.6;
}
a { color: var(--accent); text-decoration: none; }

.nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.25rem 2rem;
  max-width: 1100px;
  margin: 0 auto;
}
.logo { font-weight: 700; letter-spacing: .5px; }
.nav-links a { color: var(--muted); margin-left: 1.5rem; }
.nav-links a:hover { color: var(--fg); }

.hero {
  background: radial-gradient(1200px 500px at 50% -10%, rgba(246,130,31,.25), transparent);
  border-bottom: 1px solid var(--border);
}
.hero-content {
  max-width: 720px;
  margin: 0 auto;
  padding: 5rem 2rem 6rem;
  text-align: center;
}
.hero-content h1 { font-size: clamp(2rem, 5vw, 3.25rem); line-height: 1.15; }
.hero-content p { color: var(--muted); font-size: 1.15rem; margin: 1rem 0 2rem; }

.btn {
  display: inline-block;
  background: var(--accent);
  color: #1a1000;
  font-weight: 600;
  padding: .8rem 1.8rem;
  border-radius: 8px;
  transition: transform .15s ease, opacity .15s ease;
}
.btn:hover { transform: translateY(-2px); opacity: .95; }

.section {
  max-width: 900px;
  margin: 0 auto;
  padding: 4rem 2rem;
}
.section.alt { background: #0e131c; max-width: none; }
.section.alt > * { max-width: 900px; margin-left: auto; margin-right: auto; }
.section h2 { font-size: 1.8rem; margin-bottom: 1rem; }
.section p { color: var(--muted); }
code { background: var(--card); padding: .15rem .4rem; border-radius: 4px; color: var(--fg); }

.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 1.25rem; margin-top: 2rem; }
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.5rem;
}
.card h3 { margin-bottom: .5rem; }
.card p { color: var(--muted); font-size: .95rem; }

/* Calculator */
.calc {
  max-width: 340px;
  margin: 2rem auto 0;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 1.25rem;
  box-shadow: 0 20px 50px rgba(0, 0, 0, .35);
}
.calc-display {
  background: #0a0d13;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1rem 1.1rem;
  text-align: right;
  margin-bottom: 1rem;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}
.calc-history { color: var(--muted); font-size: .95rem; min-height: 1.2em; word-break: break-all; }
.calc-current { color: var(--fg); font-size: 2.4rem; font-weight: 600; line-height: 1.1; word-break: break-all; }

.calc-keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: .6rem;
}
.key {
  appearance: none;
  border: 1px solid var(--border);
  background: #1b2230;
  color: var(--fg);
  font-size: 1.25rem;
  font-weight: 500;
  padding: .9rem 0;
  border-radius: 12px;
  cursor: pointer;
  transition: transform .08s ease, filter .12s ease;
  user-select: none;
}
.key:hover { filter: brightness(1.15); }
.key:active { transform: scale(.94); }
.key-fn { background: #2a3242; color: var(--muted); }
.key-op { background: #f6821f; color: #1a1000; font-weight: 700; }
.key-eq { background: #f6821f; color: #1a1000; font-weight: 700; }
.key-zero { grid-column: span 2; }

.footer {
  border-top: 1px solid var(--border);
  text-align: center;
  padding: 2rem;
  color: var(--muted);
  font-size: .9rem;
}