index.css

.main-container {
  max-width: 400px;
  margin: 10vh auto 0 auto;
  border: #000 2px solid;
}
body {
  height: 100vh;
  background-color: #EDCDBB;
}
.header {
  text-align: center;
  margin-top: 4%;
  font-size: 40px;
  font-weight: 600;
  font-family: Georgia, 'Times New Roman', Times, serif;
}
.disp {
  text-align: right;
  height: 60px;
  line-height: 60px;
  padding: 20px 20px;
  font-size: 25px;
  border: 0.5px solid gray;
  color: black;
  font-weight: bold;
}
.buttons {
  grid-template-columns: 1fr 1fr 1fr 1fr;
  display: grid;
  border-bottom: 1px solid gray;
  border-left: 1px solid gray;
}
.btn {
  border: 0.5px solid gray;
  height: 60px;
  line-height: 60px;
  text-align: center;
  margin: 0.3%;
  font-size: 25px;
  cursor: pointer;
  transition: 0.5s;
  font-weight: bold;
}
.btn:hover {
  background: #000;
  color: white;

}
#equal-btn {
  background: #BF9270;
  color: white;
}