:root {
  --bg: #0a0a0f;
  --panel: #0d0d1a;
  --border: #00ffff33;
  --cyan: #00ffff;
  --magenta: #ff00ff;
  --green: #00ff41;
  --text: #e0e0ff;
  --key-bg: #111122;
  --key-fn: #1a1a2e;
  --key-op: #1a0d2e;
  --key-eq: #0d1a1a;
  --glow-cyan: 0 0 8px #00ffff, 0 0 20px #00ffff44;
  --glow-magenta: 0 0 8px #ff00ff, 0 0 20px #ff00ff44;
  --glow-green: 0 0 8px #00ff41, 0 0 20px #00ff4144;
}

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

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg);
  background-image:
    linear-gradient(rgba(0,255,255,0.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(0,255,255,0.03) 1px, transparent 1px);
  background-size: 40px 40px;
  font-family: 'Courier New', monospace;
}

.calc-wrapper {
  width: 320px;
  background: var(--panel);
  border: 1px solid var(--cyan);
  border-radius: 12px;
  padding: 20px;
  box-shadow: var(--glow-cyan), inset 0 0 30px rgba(0,255,255,0.03);
  position: relative;
  overflow: hidden;
}

.calc-wrapper::before {
  content: '';
  position: absolute;
  inset: 0;
  background: repeating-linear-gradient(
    0deg,
    transparent,
    transparent 2px,
    rgba(0, 0, 0, 0.15) 2px,
    rgba(0, 0, 0, 0.15) 4px
  );
  pointer-events: none;
  z-index: 10;
  border-radius: 12px;
}

.calc-header {
  text-align: center;
  font-size: 13px;
  letter-spacing: 6px;
  color: #444466;
  margin-bottom: 16px;
  text-transform: uppercase;
}
.calc-header span {
  color: var(--cyan);
  text-shadow: var(--glow-cyan);
  animation: flicker 4s infinite;
}

@keyframes flicker {
  0%, 95%, 100% { opacity: 1; text-shadow: var(--glow-cyan); }
  96% { opacity: 0.4; text-shadow: none; }
  97% { opacity: 1; text-shadow: var(--glow-cyan); }
  98% { opacity: 0.2; text-shadow: none; }
  99% { opacity: 1; text-shadow: var(--glow-cyan); }
}

.calc-display {
  background: #050510;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px 16px;
  margin-bottom: 16px;
  min-height: 80px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  overflow: hidden;
}

.calc-expression {
  font-size: 13px;
  color: #445566;
  min-height: 18px;
  word-break: break-all;
  text-align: right;
}

.calc-screen {
  font-size: 36px;
  color: var(--green);
  text-shadow: var(--glow-green);
  word-break: break-all;
  text-align: right;
  line-height: 1.2;
  transition: color 0.15s;
}

.calc-screen::after {
  content: '_';
  animation: blink-cursor 1s step-end infinite;
  color: var(--green);
  opacity: 1;
}

@keyframes blink-cursor {
  0%, 100% { opacity: 1; }
  50% { opacity: 0; }
}
@keyframes screen-flash {
  0%   { background: transparent; }
  30%  { background: rgba(0, 255, 255, 0.12); }
  100% { background: transparent; }
}

.calc-display.flash { animation: screen-flash 0.4s ease-out; }

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20%  { transform: translateX(-6px); }
  40%  { transform: translateX(6px); }
  60%  { transform: translateX(-4px); }
  80%  { transform: translateX(4px); }
}

.calc-screen.error {
  color: var(--magenta);
  text-shadow: var(--glow-magenta);
  animation: shake 0.4s ease-out;
}

.calc-keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.key {
  background: var(--key-bg);
  border: 1px solid #1e1e3a;
  border-radius: 8px;
  color: var(--text);
  font-size: 18px;
  font-family: inherit;
  cursor: pointer;
  padding: 16px 0;
  transition: background 0.1s, box-shadow 0.1s, transform 0.08s;
  user-select: none;
}

.key:active { transform: scale(0.93); }

@keyframes key-press-glow {
  0%   { box-shadow: 0 0 0px transparent; }
  40%  { box-shadow: 0 0 14px #00ffff, 0 0 28px #00ffff66; }
  100% { box-shadow: 0 0 0px transparent; }
}

.key.pressed { animation: key-press-glow 0.35s ease-out forwards; }

.key-fn {
  background: var(--key-fn);
  color: var(--cyan);
  border-color: #00ffff22;
}
.key-fn:hover { box-shadow: var(--glow-cyan); }

.key-op {
  background: var(--key-op);
  color: var(--magenta);
  border-color: #ff00ff22;
}
.key-op:hover { box-shadow: var(--glow-magenta); }

.key-eq {
  background: var(--key-eq);
  color: var(--cyan);
  border-color: #00ffff44;
}
.key-eq:hover { box-shadow: var(--glow-cyan); }

.key-num:hover {
  background: #1a1a2e;
  box-shadow: 0 0 6px rgba(0,255,255,0.15);
}

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

@media (max-width: 380px) {
  .calc-wrapper { width: 95vw; padding: 14px; }
  .key { font-size: 16px; padding: 14px 0; }
  .calc-screen { font-size: 28px; }
}