style.css

*{
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

.calculator{
    padding: 50px;
    background-color: #f2f2f2;
    max-width: 400px;
    margin: 0 auto;
    border: solid 1px #ccc;
    box-shadow: 0 2px 5px rgba(0,0, 0, 0.3);
    margin-top: 40px;
    border-radius: 5px;

}

#result{
    width: 100%;
    padding: 10px;
    font-size: 24px;
    border: none;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3) inset;
    border-radius: 5px;
    

}

.buttons{
   display: grid;
   grid-template-columns: repeat(4, 1fr);
   grid-gap: 10px;
   margin-top: 20px;

}

button{
  padding: 10px;
  font-size: 24px;
  border: none;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
  border-radius: 5px;
  cursor: pointer;
  transition: background-color 0.3s ease;
}

button:hover{
    background-color: #ddd;
}

.operator{
  background-color:#0074d9 ;
  color: #ffff;
}
.number, .decimal{
    background-color: #ffff;
    color: #333;
}

.clear{
  background-color: #ff4136;
  color: #ffff;
}

.equals{
    background-color: #01ff70;
   grid-row: span 3;
   color: #ffff;
}