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

@import url('https://fonts.googleapis.com/css2?family=Bebas+Neue&family=DM+Mono:wght@300;400;500&display=swap');

:root {
  --bg:         #0e0e0f;
  --surface:    #1a1a1d;
  --border:     #2e2e33;
  --accent:     #f5a623;
  --accent-dim: #c27e0f;
  --text:       #f0ede8;
  --text-muted: #7a7a82;
  --btn-num:    #242428;
  --btn-sp:     #2e2e36;
  --btn-op:     #f5a623;
  --btn-op-txt: #0e0e0f;
  --btn-eq:     #f5a623;
  --radius:     20px;
  --gap:        10px;
}

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg);
  background-image:
    radial-gradient(ellipse 60% 50% at 50% -10%, rgba(245,166,35,.15), transparent),
    repeating-linear-gradient(0deg, transparent, transparent 39px, rgba(255,255,255,.02) 40px),
    repeating-linear-gradient(90deg, transparent, transparent 39px, rgba(255,255,255,.02) 40px);
  font-family: 'DM Mono', monospace;
}

/* ── Calculator Shell ───────────────────────────── */
.calculator {
  width: 340px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px 20px 20px;
  box-shadow:
    0 0 0 1px rgba(245,166,35,.08),
    0 32px 80px rgba(0,0,0,.7),
    inset 0 1px 0 rgba(255,255,255,.06);
  position: relative;
  overflow: hidden;
}

.calculator::before {
  content: '';
  position: absolute;
  top: -60px; left: 50%;
  transform: translateX(-50%);
  width: 220px; height: 120px;
  background: radial-gradient(ellipse, rgba(245,166,35,.18), transparent 70%);
  pointer-events: none;
}

/* ── Brand ──────────────────────────────────────── */
.brand {
  font-family: 'Bebas Neue', sans-serif;
  font-size: 11px;
  letter-spacing: 5px;
  color: var(--accent);
  opacity: .6;
  text-align: right;
  margin-bottom: 12px;
}

/* ── Display ────────────────────────────────────── */
.display {
  background: rgba(0,0,0,.35);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px 18px 14px;
  margin-bottom: 18px;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  gap: 4px;
  overflow: hidden;
}

.expression {
  font-size: 13px;
  color: var(--text-muted);
  min-height: 18px;
  word-break: break-all;
  text-align: right;
  transition: opacity .2s;
}

.result {
  font-family: 'Bebas Neue', sans-serif;
  font-size: 52px;
  line-height: 1;
  color: var(--text);
  letter-spacing: 2px;
  word-break: break-all;
  transition: transform .1s ease, color .15s;
}

.result.pop {
  transform: scale(1.04);
  color: var(--accent);
}

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

/* ── Button Base ────────────────────────────────── */
.btn {
  appearance: none;
  border: none;
  cursor: pointer;
  border-radius: 14px;
  height: 68px;
  font-family: 'DM Mono', monospace;
  font-size: 20px;
  font-weight: 500;
  color: var(--text);
  background: var(--btn-num);
  border-bottom: 3px solid rgba(0,0,0,.4);
  transition:
    background .12s,
    transform .08s,
    box-shadow .12s;
  position: relative;
  overflow: hidden;
}

.btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at var(--x,50%) var(--y,50%), rgba(255,255,255,.12), transparent 60%);
  opacity: 0;
  transition: opacity .3s;
}

.btn:hover::after { opacity: 1; }

.btn:active {
  transform: translateY(2px);
  border-bottom-width: 1px;
}

/* ── Special (AC, +/−, %) ───────────────────────── */
.btn.special {
  background: var(--btn-sp);
  color: var(--accent);
}

/* ── Operators ──────────────────────────────────── */
.btn.operator {
  background: var(--btn-op);
  color: var(--btn-op-txt);
  font-size: 24px;
  font-weight: 700;
  border-bottom-color: var(--accent-dim);
}

.btn.operator:hover {
  background: #f7b740;
}

.btn.operator.active {
  background: var(--text);
  color: var(--accent);
  box-shadow: 0 0 0 2px var(--accent);
}

/* ── Equals ─────────────────────────────────────── */
.btn.equals {
  background: var(--btn-eq);
  color: var(--btn-op-txt);
  font-size: 26px;
  font-weight: 700;
  border-bottom-color: var(--accent-dim);
}

.btn.equals:hover { background: #f7b740; }

/* ── Wide (0) ───────────────────────────────────── */
.btn.wide {
  grid-column: span 2;
  text-align: left;
  padding-left: 26px;
}

/* ── Ripple cursor tracking ─────────────────────── */
.btn { --x: 50%; --y: 50%; }