.marvel-device {
    align-content: center;
    position: absolute;
    top: 5%;
    
    left: 50%;
    margin-left: -183px;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.calc {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-row-gap: 5px;
    color: white;
    background-color: black;
    align-items: stretch;
    height: 100%;
}

.output {
    grid-column: span 4 / auto;
    height: 85px;
    line-height: 90px;
    text-align: right;
    font-size: 50px;
}

.button.digit-zero {
    grid-column: span 2 / auto;
    width: 140px; 
    border-radius: 50px;
}

.button {    
    width: 70px;
    height: 70px;
    cursor: pointer;
    border-radius: 50%;  
    justify-self: center;
    line-height: 70px;    
    text-align: center;

    font-size: 35px;

    border: 2px solid #000;   
    

    -webkit-touch-callout: none; /* iOS Safari */
    -webkit-user-select: none; /* Safari */
     -khtml-user-select: none; /* Konqueror HTML */
       -moz-user-select: none; /* Firefox */
        -ms-user-select: none; /* Internet Explorer/Edge */
            user-select: none; /* Non-prefixed version, currently
                                  supported by Chrome and Opera */    
}

.button.command {
    background-color: gray;
    color: black;
}

.button.digit {
    background-color: rgb(48, 48, 48);
    font-weight: 400;  
}

.button.operation {
    background-color: orange;    
    font-weight: 600;  
}

.button.operation.checked {
    background-color: #fff;
    color: #000;
    /* font-weight: 600;  */
}

.button.button.operation:hover {
    filter: brightness(130%) grayscale(50%);
    /* 
      box-shadow: inset 0 0 0 3px antiquewhite;     
    */
}

.button:hover {
    filter: brightness(180%);
    /* 
      box-shadow: inset 0 0 0 3px antiquewhite;     
    */
}

.button:active {
    background-color: lightyellow;
    color: #000;
}