Primeflex, "lock in" width length after adjusting using "rem"

I have table headers, one of there looks something like:

<th rowspan="4" class="w-6rem">Header Title</th>

the table looks fine on a full screen but when adjusted it stays on one column and all the letters are vertical. how can i keep the "w-6rem" after adjusting the screen size to a smaller one?

the table header and the sizing classes are all based on the primeflex documentation