:root {
  color-scheme: dark;
  --bg: #0c1117;
  --panel: #111b26;
  --panel-border: #2b3a4f;
  --text: #e5edf5;
  --text-muted: #9cb0c4;
  --danger: #fca5a5;
  --accent: #47a3ff;
  --accent-strong: #1d6fca;
  --button: #263648;
  --button-hover: #304359;
  --fn: #3f3530;
  --fn-hover: #544439;
  --op: #23435a;
  --op-hover: #2e5774;
  --control: #3e2d2d;
  --control-hover: #513c3c;
  --const: #2f3744;
  --const-hover: #404b5b;
  --num: #263648;
  --num-hover: #32465d;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Segoe UI", Roboto, Arial, sans-serif;
  min-height: 100vh;
  display: grid;
  place-items: center;
  background:
    radial-gradient(1200px 500px at 20% -20%, rgba(71, 163, 255, 0.12), transparent 50%),
    linear-gradient(180deg, #0d141d 0%, #090f16 100%);
  color: var(--text);
  padding: 1rem;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image: linear-gradient(rgba(255, 255, 255, 0.025) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.025) 1px, transparent 1px);
  background-size: 28px 28px;
}

.calculator {
  width: min(460px, 96vw);
  padding: 1.1rem;
  border-radius: 16px;
  border: 1px solid var(--panel-border);
  background: linear-gradient(180deg, rgba(28, 42, 59, 0.92) 0%, rgba(14, 23, 33, 0.95) 100%);
  box-shadow:
    0 20px 45px rgba(0, 0, 0, 0.45),
    inset 0 1px 0 rgba(255, 255, 255, 0.05);
  position: relative;
  z-index: 1;
}

.calculator-header {
  margin-bottom: 0.9rem;
}

h1 {
  margin: 0;
  font-size: 1.35rem;
  font-weight: 600;
  letter-spacing: 0.02em;
}

.subtitle {
  margin: 0.3rem 0 0;
  color: var(--text-muted);
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
}

.display-shell {
  background: linear-gradient(180deg, #0b131c 0%, #0e1722 100%);
  border: 1px solid #2d3a49;
  border-radius: 12px;
  padding: 0.65rem;
  margin-bottom: 0.85rem;
}

#display {
  width: 100%;
  font-size: 1.3rem;
  padding: 0.7rem;
  border: 1px solid #314559;
  border-radius: 8px;
  text-align: right;
  background: #060b10;
  color: #f2f8ff;
  box-shadow: inset 0 1px 6px rgba(0, 0, 0, 0.45);
}

.meta-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  margin-top: 0.55rem;
}

#status,
#mode {
  margin: 0;
  font-size: 0.78rem;
  min-height: 1rem;
}

#mode {
  color: #9fcbff;
}

#status {
  color: var(--danger);
  text-align: right;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 0.45rem;
}

button {
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: 8px;
  padding: 0.7rem 0.45rem;
  font-size: 0.96rem;
  cursor: pointer;
  background: var(--button);
  color: var(--text);
  transition: background-color 0.16s ease, transform 0.06s ease;
}

button:hover {
  background: var(--button-hover);
}

button:active {
  transform: translateY(1px);
}

.btn-fn {
  background: var(--fn);
}

.btn-fn:hover {
  background: var(--fn-hover);
}

.btn-op {
  background: var(--op);
}

.btn-op:hover {
  background: var(--op-hover);
}

.btn-control {
  background: var(--control);
}

.btn-control:hover {
  background: var(--control-hover);
}

.btn-const {
  background: var(--const);
}

.btn-const:hover {
  background: var(--const-hover);
}

.btn-num {
  background: var(--num);
}

.btn-num:hover {
  background: var(--num-hover);
}

.equals {
  grid-column: 1 / -1;
  background: linear-gradient(180deg, var(--accent) 0%, var(--accent-strong) 100%);
  color: #f8fbff;
  font-weight: 700;
  letter-spacing: 0.06em;
}

.equals:hover {
  background: linear-gradient(180deg, #58b0ff 0%, #267fd8 100%);
}

.hint {
  margin: 0.75rem 0 0;
  color: var(--text-muted);
  text-align: center;
  font-size: 0.74rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

@media (max-width: 480px) {
  .calculator {
    padding: 0.9rem;
    border-radius: 14px;
  }

  button {
    padding: 0.62rem 0.35rem;
    font-size: 0.88rem;
  }

  h1 {
    font-size: 1.2rem;
  }
}