For that you can use table-layout: fixed; for your table and give any width to table check this
Add your css in Asset->theme.scss file.
If you cant let me know with store URL.
Try to add table-layout: auto; to this table because some of other css affected.
I have checked your store and table looking fine. Whats an issue send me screenshot so i can understand better. And yes you have to add this css for all table.