style.css

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f0f0f0;
    margin: 0;
    font-family: Arial, sans-serif;
  }
  
.maincontainer{
    width: 340px;
    height: auto;
    border: 1px solid #100e0e;
    background-color: #fff;
}
.screen{
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px solid #100e0e;
    height: 50px;
    background-color: #222;
    padding: 0 10px;
    border-top-left-radius: 10px;
    border-top-right-radius: 10px;
    color: #fff;
}
.buttons{
    display: grid;
    grid-template-columns: repeat(4,1fr);
    gap: 10px;
    padding: 10px;
}

.buttons div{
    height: 50px;
    background-color: #ddd;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.5rem;
    border:1.5px solid bisque;
    cursor: pointer;
}

.buttons div:hover{
    background-color: #999;
}

.buttons div:active{
    background-color: #3f3f3f;
}