body{
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f8f9fa;
}

.calculator{
    font-family: Arial, sans-serif;
    background-color: #212529;
    max-height: 600px;
    max-width: 500px;
    border-radius: 15px;
    overflow: hidden;
}
#display{
    width: 100%;
    padding: 10px;
    font-size: 4rem;
    text-align: left;
    background-color: #343a40;
    color: white;
}
.keys{
    display: grid;
    grid-template-columns: repeat(4,1fr);
    gap:10px;
    padding: 25px;
}

button{
    height: 80px;
    width: 80px;
    border-radius: 50%;
    border: none;
    background-color: #343a40;
    color: white;
    font-size: 1.75rem;
    font-weight: bold;
    cursor: pointer;
    transition: 0.5s ease-out;
}
button:hover{
    background-color: #6c757d;
}
button:active{
    background-color: #6c757d;
}
.opr-btn{
    background-color: #ffbd00;
}
.opr-btn:hover{
    background-color: #ffbd00;
}