body {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #f0f0f0;
  margin: 0;
}

.calculator {
  width: 100%;
  max-width: 320px;
  padding: 1em;
  background: #1a1919;
  border-radius: 10px;
  box-shadow: #b4e8ea 0px 0px 5px;
}

.display {
  width: 90%;
  padding: 0.75em;
  font-size: 1.5em;
  text-align: right;
  border: none;
  border-radius: 5px;
  margin-bottom: 1em;
  background: #ffff;
  box-shadow: #b4e8ea 0px 0px 5px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.5em;
}

.btn {
  padding: 1em;
  font-size: 1.2em;
  background: #444444;
  color: rgb(67, 229, 229);
  border: none;
  border-radius: 5px;
  cursor: pointer;
  box-shadow: #b4e8ea 0px 0px 5px;
}

.btn:hover {
  background: #666666;
}

.btn_add{
    height: 200%;
    padding: 23px;
}
.btn_equal{
    width: 211%;
}