*, *::after, *::before{
    box-sizing: border-box;
    font-family:Verdana, Geneva, Tahoma, sans-serif;
    font-weight: normal;
}

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

.container{
    display: grid;
    justify-content: center;
    align-content: center;
    height: 100vh;
    grid-template-columns: repeat(4, 70px);
    grid-template-rows: minmax(70px, auto) repeat(5, 70px);
}

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

.container > 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: 10px;
}

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

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