:root {
  --number-btn-color: #333333;
  --operator-btn-color: #FE9500;
  --alt-btn-color: #a5a5a5;
}

*, *::after, *::before {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: linear-gradient(#25375a, #0C1524);
  background-size: cover;
  min-height: 100vh;
  font-family: 'Share Tech Mono', monospace;
}

button {
  background-color: var(--number-btn-color);
  color: white;
  font-size: 1.5rem;
  border: none;
  font-family: inherit;
}

button:hover {
  font-size: 2rem;
}

button:active {
  font-size: 1.5rem;
}

.bold {
  font-weight: bold;
}

.container {
  padding-top: 3rem;
  margin: 0 auto;
  width: 80%;
  max-width: 600px;
}

.keypad > *, .display > * {
  outline: 4px solid #575757;
}

.display {
  display: grid;
  grid-template-columns: 3fr 1fr;
  grid-auto-rows: 80px;
}

.display__result {
  height: 60%;
}

.display__current {
  height: 40%;
}

.display__result, 
.display__current {
  font-size: 1.3rem;
  display: grid;
  align-items: center;
  text-align: end;
  padding-right: 0.5em;
}

.display__current {
  background-color: #efefef;
}

.display__result {
  background-color: #fed07a;
}

.keypad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-auto-rows: 60px;
}

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

.alt-btn {
  background-color: var(--alt-btn-color);
  color: black;
}

/* media query */

@media (min-width:500px) {
  html {
    font-size: 20px;
  }

  .display {
    grid-auto-rows: 100px;
  }

  .keypad {
    grid-auto-rows: 80px;
  }
}

@media (min-width:600px) {
  html {
    font-size: 22px;
  }

  .display {
    grid-auto-rows: 120px;
  }

  .keypad {
    grid-auto-rows: 100px
  }
}