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

body{
    padding: 0;
    margin: 0;
    background: url(pic1.jpg);
    background-position:center center;
	background-repeat:no-repeat;
	background-size:cover;
	background-attachment: fixed;
	text-align: center;
	justify-content: center;
}

h1{
    color: whitesmoke;
    border: 5px solid black;
}

.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: black;
    display: flex;
    align-items: flex-end;
    justify-content: space-around;
    flex-direction: column;
    padding: 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: 1.5rem;
}