How to adjust table column width with CSS

HELLO.
Site that im working on , contains many products and each product has its own Specification table that are being imported into database. I need to change the column width of the table using CSS . i can not go to each product and change tables properties .. i used
td:nth-child(1) in the css file. using this i can change many properties in the table but width of the column is not changing ? would appreciate any info on this . bellow is the link to a page….

How to adjust table column width with CSS