:root {
  --bg: #0f172a;
  --surface: #111827;
  --surface-2: #1f2937;
  --text: #e5e7eb;
  --muted: #94a3b8;
  --accent: #f59e0b;
  --accent-2: #22c55e;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Inter, system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  background: radial-gradient(circle at top, #1e293b, var(--bg));
  color: var(--text);
}

.app-shell {
  max-width: 1100px;
  margin: 2rem auto;
  padding: 1.5rem;
}

.app-header h1 {
  margin: 0;
}

.app-header p {
  color: var(--muted);
  margin-top: 0.5rem;
}

.tabs {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 0.75rem;
  margin: 1.25rem 0;
}

.tab-btn {
  border: 1px solid #374151;
  color: var(--text);
  background: var(--surface);
  padding: 0.8rem;
  border-radius: 0.65rem;
  font-weight: 700;
  cursor: pointer;
}

.tab-btn.active {
  background: linear-gradient(90deg, #f59e0b, #f97316);
  color: #111827;
  border-color: transparent;
}

.panel {
  display: none;
  background: rgba(17, 24, 39, 0.92);
  border: 1px solid #374151;
  border-radius: 1rem;
  padding: 1.2rem;
}

.panel.active {
  display: block;
}

.display {
  width: 100%;
  padding: 0.85rem;
  font-size: 1.35rem;
  border-radius: 0.6rem;
  border: 1px solid #4b5563;
  background: #0b1220;
  color: #f8fafc;
  margin-bottom: 1rem;
}

.key-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(64px, 1fr));
  gap: 0.55rem;
}

button {
  border: none;
  border-radius: 0.6rem;
  padding: 0.75rem;
  font-size: 1rem;
  font-weight: 700;
  background: var(--surface-2);
  color: var(--text);
  cursor: pointer;
}

button:hover {
  filter: brightness(1.12);
}

.operator-btn {
  background: #374151;
}

.equal-btn {
  background: var(--accent-2);
  color: #052e16;
}

.helper,
.result-line {
  color: var(--muted);
}

.scientific-grid {
  margin-bottom: 0.75rem;
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
}

.tool-card {
  border: 1px solid #334155;
  border-radius: 0.9rem;
  padding: 1rem;
  background: #0b1220;
}

.tool-card h3 {
  margin-top: 0;
}

label {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  font-size: 0.9rem;
  color: var(--muted);
  margin-bottom: 0.7rem;
}

input[type="number"] {
  background: #1e293b;
  border: 1px solid #475569;
  border-radius: 0.45rem;
  color: var(--text);
  padding: 0.6rem;
}

@media (max-width: 640px) {
  .app-shell {
    margin: 1rem auto;
    padding: 0.85rem;
  }

  .key-grid {
    grid-template-columns: repeat(4, 1fr);
  }
}