style.css

*{
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
body{
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}
.container{
  background-color: rgb(153, 153, 173);
  display: grid;
  grid-template-columns:repeat(4,90px) ;
  grid-template-rows:repeat(6,90px) ;
  border: 10px groove rgb(255, 244, 228);
}
.output_area{
  font-size: 20px;
  text-align: right;
  grid-column: 1/ -1;
  background-color: rgb(238, 238, 238);
  border: 1px solid black;
  overflow-x: hidden;
}

button{
border-radius: 8px;
font-size: 30px;
text-transform: uppercase;
outline: none;
border:1px solid burlywood;
margin: 4px 2px;
}

button:nth-child(5){
 background-color: hsl(180, 97%, 40%);

 /* border-radius: 100%; */
}
button:nth-child(9){
 background-color: hsl(180, 100%, 14%);
 /* border-radius: 100%; */
}
button:nth-child(13){
 background-color: hsl(180, 97%, 40%);
 /* border-radius: 100%; */
}
button:nth-child(17){
 background-color: hsl(180, 100%, 14%);
  /* border-radius: 100%; */
}
button:nth-child(21){
 background-color: hsl(180, 97%, 40%);
  /* border-radius: 100%; */
}