body {
    margin: 10px;
}

#letters {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
}

#letters button, #letters .invisible {
    margin: 5px 8px;
    flex-grow: 0;
    width: 51px;
    height: 25px;
    color: black;
    background-color: lightgray;
}


#letters button {
    cursor: pointer;
}

#letters .invisible {
    margin-top: 0;
    margin-bottom: 0;
    height: 0;
}

#letters button.selected {
    color: white;
    background-color: blue;
}

div > #showWords {
    margin: 10px 8px;
}

#showWords {
    clear: both;
}

#words {
    list-style-type: none;
    margin: 10px 8px;
    padding: 0;
}
#words li {
    margin: 0;
    padding: 0;
}



@media (min-width: 360px) {
    #words {
        column-count: 3;
    }
}

@media (min-width: 450px) {
    #words {
        column-count: 3;
    }
}

@media (min-width: 600px) {
    #words {
        column-count: 4;
    }
}

@media (min-width: 750px) {
    #words {
        column-count: 5;
    }
}

@media (min-width: 900px) {
    #words {
        column-count: 6;
    }
}