style.css

*::after,*::before,*{
    margin: 0px;
    padding: 0px;
    box-sizing: border-box;
    font-family: poppins, sans-serif;
}

.calculator_grid{
    background: linear-gradient(to right, #223, #113);
    min-height: 100vh;
    display: grid;
    justify-content: center;
    align-content: center;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: minmax(100px, auto) repeat(5 ,100px);
}
button{
    background-color: rgba(0, 0, 0, .70) !important;
    border: 1px solid black;
    color: white;
    font-size: 1.3rem;
    font-weight: 500;
    cursor: pointer;
}
button:hover {
    background-color: black !important;
}
button:active {
    background-color: rgba(0, 0, 0, .9) !important;
}
.screen{
    grid-column: 1 / -1;
    word-wrap: break-word;
    word-break: break-all;
}
.span_2{
    grid-column: span 2;
}
.screen{
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    padding: 10px;
    color: white;   
    background-color: rgba(0, 0, 0, .9);
    border-bottom: 4px solid black;
    justify-content: space-between;
}
.current_operand{
    font-size: 2rem;
}