:root {
  --bg-start: #f7efe5;
  --bg-end: #c6d8d3;
  --panel: rgba(20, 28, 36, 0.92);
  --panel-edge: rgba(255, 255, 255, 0.14);
  --display-bg: rgba(255, 255, 255, 0.08);
  --text-main: #f9fbfa;
  --text-soft: #bfd0ca;
  --button: rgba(255, 255, 255, 0.08);
  --button-hover: rgba(255, 255, 255, 0.16);
  --button-muted: #314956;
  --operator: #ff8a3d;
  --equals: #6fcf97;
  --shadow: 0 24px 60px rgba(0, 0, 0, 0.24);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-items: center;
  font-family: "Space Grotesk", sans-serif;
  background:
    radial-gradient(circle at top, rgba(255, 255, 255, 0.55), transparent 30%),
    linear-gradient(135deg, var(--bg-start), var(--bg-end));
  color: var(--text-main);
}

.page-shell {
  width: min(100%, 480px);
  padding: 24px;
}

.calculator {
  padding: 24px;
  border: 1px solid var(--panel-edge);
  border-radius: 28px;
  background: var(--panel);
  -webkit-backdrop-filter: blur(18px);
  backdrop-filter: blur(18px);
  box-shadow: var(--shadow);
}

.display-panel {
  margin-bottom: 20px;
  padding: 20px;
  border-radius: 20px;
  background: var(--display-bg);
}

.calculator-title {
  margin: 0 0 12px;
  font-size: 0.9rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-soft);
}

.display {
  min-height: 72px;
  display: flex;
  align-items: flex-end;
  justify-content: flex-end;
  font-size: clamp(2rem, 5vw, 3.3rem);
  font-weight: 700;
  text-align: right;
  word-break: break-all;
}

.button-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 14px;
}

.btn {
  border: none;
  border-radius: 18px;
  min-height: 68px;
  font: inherit;
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text-main);
  background: var(--button);
  cursor: pointer;
  transition: transform 0.18s ease, background 0.18s ease, box-shadow 0.18s ease;
}

.btn:hover {
  background: var(--button-hover);
  transform: translateY(-2px);
}

.btn:active {
  transform: translateY(1px);
}

.btn-muted {
  background: var(--button-muted);
}

.btn-operator {
  background: var(--operator);
  color: #17212b;
}

.btn-equals {
  background: var(--equals);
  color: #0d1b17;
}

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

@media (max-width: 420px) {
  .page-shell {
    padding: 16px;
  }

  .calculator {
    padding: 18px;
    border-radius: 22px;
  }

  .btn {
    min-height: 60px;
  }
}