How to modify css to influence index page

Actually, I am new in opencart. Even though I have watched some tutorial videos about that but still not familiar with that. My question is how to adjust the Footer information section left margin. I found there is a codemanager in System section. When I modify the code in address: catalog/view/theme/default/templete/common/footer.twig. I found there is no use when I modify this part of code. Does I Ignore some other problems or I modify the wrong path.

By the way, I can see I am using default theme in store.

You can locate stylesheet.css to edit footer.

Thx bro. But I change the margin-top: 30 px to 50 px. The page seems no change then. Is the stylesheet.css located at catalog/view/theme/default/stylesheet/stylesheet.css?

Hold down Ctrl and press F5 to hard refresh.

I tried to press crtl + F5. But still no change. Do I need to change some settings in my opencart?