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

body {
  background: #000;
  color: #fff;
  font-family: Arial, sans-serif;
  
  min-height: 100vh;
  
  display: flex;
  justify-content: center;
  align-items: center;
  
  padding: 20px;
}

.calculator {
  width: 100%;
  max-width: 420px;
}

h1 {
  text-align: center;
  
  color: #fff;
  
  font-size: 28px;
  margin-bottom: 25px;
  
  font-weight: bold;
}

#display {
  width: 100%;
  
  height: 125px;
  
  background: #000;
  
  color: #fff;
  
  border: 2px solid #fff;
  
  border-radius: 20px;
  
  padding: 20px;
  
  font-size: 42px;
  
  text-align: right;
  
  outline: none;
  
  margin-bottom: 20px;
}

.buttons {
  display: grid;
  
  grid-template-columns:
    repeat(4, 1fr);
  
  gap: 12px;
}

.buttons button {
  min-height: 68px;
  
  background: #000;
  
  color: #fff;
  
  border: 2px solid #fff;
  
  border-radius: 16px;
  
  font-size: 22px;
  
  font-weight: bold;
  
  cursor: pointer;
  
  transition:
    transform 0.08s,
    background 0.15s;
}

.buttons button:active {
  transform: scale(0.94);
  
  background: #222;
}

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

#display::placeholder {
  color: #fff;
}

/* Voice button created by script.js */

.voice-button {
  grid-column: span 4;
  
  width: 100%;
  
  min-height: 60px;
  
  margin-top: 4px;
  
  background: #000;
  
  color: #fff;
  
  border: 2px solid #fff;
  
  border-radius: 16px;
  
  font-size: 22px;
  
  font-weight: bold;
}

@media (max-width: 420px) {
  
  body {
    padding: 15px;
  }
  
  h1 {
    font-size: 25px;
  }
  
  #display {
    height: 110px;
    
    font-size: 36px;
  }
  
  .buttons {
    gap: 10px;
  }
  
  .buttons button {
    min-height: 62px;
    
    font-size: 20px;
  }
}