/* VUNA-Calc — Styles */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
 
body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #0a1f0a;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}
 
.calculator {
  background: #0d2b0d;
  border-radius: 20px;
  padding: 24px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
  width: 320px;
}
 
.brand {
  text-align: center;
  color: #4ade80;
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 3px;
  margin-bottom: 16px;
  text-transform: uppercase;
}
 
.display {
  background: #14381a;
  border-radius: 12px;
  padding: 16px 20px;
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  font-size: 32px;
  font-weight: 300;
  color: #e2e2e2;
  word-break: break-all;
  margin-bottom: 20px;
  transition: color 0.2s;
}
 
.display.error { color: #f87171; }
 
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}
 
.btn {
  height: 64px;
  border: none;
  border-radius: 12px;
  font-size: 20px;
  font-weight: 500;
  cursor: pointer;
  transition: transform 0.1s, opacity 0.1s;
  background: #14381a;
  color: #e2e2e2;
}
 
.btn:active { transform: scale(0.94); opacity: 0.8; }
 
.btn.action  { background: #166534; color: #fff; }
.btn.operator{ background: #4ade80; color: #000; }
.btn.equals  { background: #4ade80; color: #000; grid-column: span 2; }
.btn.custom  { background: #166534; color: #fff; font-size: 16px; }
 
.btn:hover { opacity: 0.85; }