/* ============================================================
   Olivia Nneka Anigbogu — SEN 482 Calculator
   Aesthetic: dark editorial, monospaced display, clean grid
   ============================================================ */

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

:root {
  --bg: #0f0f0f;
  --surface: #1a1a1a;
  --border: #2a2a2a;
  --num-bg: #242424;
  --num-hover: #2e2e2e;
  --op-bg: #1e2a3a;
  --op-hover: #243348;
  --op-color: #5b9cf6;
  --ac-bg: #2a1a1a;
  --ac-color: #f87171;
  --eq-bg: #5b9cf6;
  --eq-hover: #4a87e0;
  --prime-bg: #1a2a1a;
  --prime-color: #4ade80;
  --prime-hover: #243b24;
  --text: #f0f0f0;
  --muted: #666;
  --display-font: "DM Mono", monospace;
  --ui-font: "DM Sans", sans-serif;
  --radius: 12px;
  --gap: 8px;
}

body {
  background: var(--bg);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--ui-font);
  padding: 20px;
}

/* ── Wrapper ── */
.wrapper {
  width: 100%;
  max-width: 360px;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

/* ── Header ── */
.header {
  text-align: center;
  padding: 4px 0 8px;
}

.header-name {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.header-sub {
  font-size: 0.7rem;
  color: var(--muted);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-top: 2px;
}

/* ── Card ── */
.calc-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 20px;
  box-shadow: 0 24px 60px rgba(0, 0, 0, 0.6);
}

/* ── Display ── */
.display-wrap {
  background: #111;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin-bottom: 12px;
  min-height: 72px;
  display: flex;
  align-items: flex-end;
  justify-content: flex-end;
  overflow: hidden;
}

.display-expr {
  font-family: var(--display-font);
  font-size: 2.2rem;
  font-weight: 500;
  color: var(--text);
  text-align: right;
  word-break: break-all;
  line-height: 1.1;
  transition: font-size 0.15s ease;
}

/* Shrink text when it gets long */
.display-expr.long {
  font-size: 1.6rem;
}
.display-expr.xlong {
  font-size: 1.2rem;
}

/* ── Prime Banner ── */
.prime-banner {
  display: none;
  align-items: center;
  gap: 8px;
  background: var(--prime-bg);
  border: 1px solid #2d4a2d;
  border-radius: 10px;
  padding: 10px 14px;
  margin-bottom: 12px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--prime-color);
  letter-spacing: 0.03em;
  animation: fadeIn 0.25s ease;
}

.prime-banner.show {
  display: flex;
}
.prime-banner.not-prime {
  background: #2a1e1a;
  border-color: #4a2e1a;
  color: #fb923c;
}
.prime-banner.error {
  background: #2a1a1a;
  border-color: #4a1a1a;
  color: #f87171;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(-4px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* ── Button Grid ── */
.btn-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--gap);
}

/* ── Buttons base ── */
.btn {
  border: none;
  border-radius: var(--radius);
  font-family: var(--ui-font);
  font-size: 1rem;
  font-weight: 600;
  height: 64px;
  cursor: pointer;
  transition:
    background 0.12s ease,
    transform 0.08s ease,
    box-shadow 0.12s ease;
  position: relative;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.btn:active {
  transform: scale(0.94);
}

/* Number buttons */
.btn-num {
  background: var(--num-bg);
  color: var(--text);
}
.btn-num:hover {
  background: var(--num-hover);
}

/* Zero spans 2 cols */
.btn-zero {
  grid-column: span 2;
}

/* Operator buttons */
.btn-op {
  background: var(--op-bg);
  color: var(--op-color);
  font-size: 1.2rem;
}
.btn-op:hover {
  background: var(--op-hover);
}

/* AC / backspace */
.btn-action {
  background: var(--ac-bg);
  color: var(--ac-color);
}
.btn-action:hover {
  background: #331f1f;
}

/* Prime button */
.btn-prime {
  background: var(--prime-bg);
  color: var(--prime-color);
  font-size: 0.78rem;
  letter-spacing: 0.04em;
  border: 1px solid #2d4a2d;
}
.btn-prime:hover {
  background: var(--prime-hover);
}

/* Equals */
.btn-eq {
  background: var(--eq-bg);
  color: #fff;
  font-size: 1.3rem;
  box-shadow: 0 4px 20px rgba(91, 156, 246, 0.35);
}
.btn-eq:hover {
  background: var(--eq-hover);
  box-shadow: 0 6px 24px rgba(91, 156, 246, 0.45);
}

/* ── Error state on display ── */
.display-expr.error {
  color: #f87171;
}

/* ── Responsive ── */
@media (max-width: 400px) {
  .btn {
    height: 58px;
    font-size: 0.95rem;
  }
  .display-expr {
    font-size: 1.9rem;
  }
}