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

.container {
  background-color: #ddd;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  background-color: #202020;
  width: 350px;
  padding: 3px;
  border-radius: 6px;
  box-shadow: 2px 4px 4px rgb(0 0 0 / 19%);
  position: relative;
}

h1 {
  position: absolute;
  top: -100px;
  text-align: center;
  left: 50%;
  width: 100%;
  transform: translateX(-50%);
  font-size: 40px;
}

.calculator #display {
  width: 100%;
  height: 90px;
  text-align: right;
  padding: 5px;
  font-size: 35px;
  background: none;
  border: none;
  outline: none;
  color: white;
}
.calculator > div {
  display: flex;
  gap: 3px;
}
.calculator > div button {
  flex: 1;
  height: 70px;
  border: none;
  outline: none;
  border-radius: 4px;
  margin-top: 3px;
  background-color: #3b3b3b;
  color: white;
  cursor: pointer;
  font-size: 20px;
  transition: 0.3s;
}
.calculator > div button:not(.equal):hover {
  background-color: #323232;
}
.calculator > div button.choosen {
  background-color: #323232;
}
.calculator > div button.operator {
  font-size: 30px;
}
.calculator > div button.equal {
  background-color: #02c4b2;
  font-size: 30px;
}
.calculator > div button.equal:hover {
  background-color: #02a495;
}