I don’t think you need to completely remove the margins from the entire website, unless your goal is to reuse a css assembled without margins. Without paddings and margins the page will look worse.
As a trick you can right click anywhere on the web and find where the margin is being invoked (possibly in a div at the top of the code).
What I do in my pages is to remove the margins only for some sections of the web. It is not the best way but it is a solution. I attach an image for you to see how it works.
You can see the example directly inspecting the element in this web
`margin-left: -6rem; margin-right: -6rem; padding-left: 6rem; padding-right: 6rem;`