*, *:before, *::after {
    box-sizing: border-box;
    font-family: Arial, Helvetica, sans-serif;
    font-weight: normal;

}

body {
    padding: 0;
    margin: 0;
    background: linear-gradient(to right, #00aaff, #00ff6c);
}

.calculator-grid{
    display: grid;
    justify-content: center;
    align-content: center;
    min-height: 100vh;
    grid-template-columns: repeat(4,100px);
    grid-template-rows: minmax(120px, auto) repeat(5,100px);
}

.calculator-grid > button {
    cursor: pointer;
    font-size: 2rem;
    border: 1px solid white;
    outline: none; 
    background-color: rgba(255,255,255, .75) ;
}

.calculator-grid > button:hover {
    background-color: rgba(255,255,255, .9) ;
}

.span-two {
    grid-column: span 2;

}

.output {
    grid-column: 1/-1;
    background-color: rgba(0,0,0,.75);
    display: flex;
    align-items: flex-end;
    justify-content: space-around;
    flex-direction: column;
    padding-left: 10px;
    word-wrap: break-word;
    word-break: break-all;

}

.output .previous-operand {
    color: rgba(255,255,255, .75);
    font-size: 1.5rem;
}

.output .current-operand {
    color: white;
    font-size: 2.5rem;
}