Full-width front page & post

I was able to remove the sidebar column from your fantastic advice on prior threads, and even got the text/images centered.

But I cannot find the way to edit the code files to make the new single-column full-width, or at least a bit wider.

I tried adding Custom CSS in the Theme Customization, per advice on another forum, and expanding the Media Width to 1000 pixels in the same area, but it didn’t make a difference:

.content-area {
width: 100%;
margin: 0px;
border: 0px;
padding: 0px;
}

.content-area .site {
margin:0px;
}