Button won’t center align mystery

Hi

I’m trying to learn CSS and stuck on one final mystery to solve with an Elementor cart button.

In the mobile version of this page there is a sticky ADD TO BASKET button at the bottom of the page but for some reason I cannot get it to center align.

Have tried all the obvious CSS stuff like

align-items: center;

Using elementor combined with my own custom CSS but can’t fixt it!

It is in the footer to make sure its at the bottom of the page and fine when in the page area but when I place it in the footer it aligns left and can’t get into center align.

If any expert out there could take a look it would be much appreciated?

Many Thanks,

James

The page I need help with: [log in to see the link]