html {
  background-color: #61DAFB;
}
#app {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-auto-rows: minmax(50px, auto);
  font-size: 28px;
  width: 400px;
  margin: 0 auto;
}
.display {
  grid-column: 1/5;
  background-color: #333;
  color: white;
  text-align: center;

}

#heading {
  color: #000;
  margin: 0 auto;
  width: 100px;
}

.zero {
  grid-column: 1/3;
  text-align: center;
  cursor: pointer;
}

.btn {
  background-color: #f2f2f2;
  border: 1px solid #333;
  text-align: center;
}

.btn-number:hover {
  background-color: #fff;
  color: black;
  cursor: pointer;
}

.operator {
  background-color: orange;
  cursor: pointer;
}


.me {
  font-size: 18px;
  color: #000;
}

a:hover {
  cursor: pointer;
}