@media screen and (width <= 600px) {
    .completedPuzzlesColumnHeader, .completedPuzzlesColumnValue {
        display: none;
    }
}
@media screen and (width <= 500px) /* Breakpoint: MOBILE */ {
    .avgTimeColumnHeader, .avgTimeColumnValue, .avgScoreColumnHeader, .avgScoreColumnValue {
        display: none;
    }
}