What is responsible for the width of this menu? How to stretch it to the full width of the block?

Question

css

There is a menu on the page bat.shsa.ru/index1.html , I can't figure out how to stretch it to the entire width of the menu block. Explain to a noob please.

Answer 1

the ul element has a width of 50% of the parent block. And with margin, it's centered.