* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  min-height: 100vh;
  background-color: aliceblue;
  display: flex;
  justify-content: center;
  align-items: center;
  text-align: center;
}
.calculator {
  width: 300px;
  height: 491px;
  box-shadow: 5px 5px 20px rgba(0, 0, 0, 0.6);
  border-radius: 10px;
  background-color: rgb(40, 39, 39);
  overflow: hidden;
}
form input {
  width: 100%;
  height: 150px;
  background-color: #000;
  border: none;
  border-radius: 10px;
  pointer-events: none;
  font-size: 2rem;
  padding: 1rem;
  color: #fff;
  text-align: right;
}
.buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  padding: 20px;
}
button {
  width: 60px;
  height: 50px;
  border: 1px solid black;
  border-radius: 5px;
  font-size: 22px;
  font-weight: 600;
  cursor: pointer;
  flex: 0 0 22%;
  margin: 5px 0;
}
.btn-yellow {
  background-color: rgb(158, 158, 78);
}
.btn-yellow:hover {
  background-color: rgb(142, 142, 64);
}
.btn-grey {
  background-color: rgb(214, 205, 205);
}
.btn-grey:hover {
  background-color: rgb(197, 189, 189);
}
.btn-equal {
  background-color: green;
}
.btn-equal:hover {
  background-color: rgb(5, 109, 5);
}
.btn-clear {
  background-color: red;
}
.btn-clear:hover {
  background-color: rgb(226, 20, 20);
}