Styling the background of a block inside a parent with margins so that the color ignores margins: https://css-tricks.com/the-inside-problem/

The behavior of grid gap: https://ryanmulligan.dev/blog/grid-gap/

I don’t use grid gap on the single-column version of this site because it doesn’t collapse for empty cells, so there’s a disproportionate amount of whitespace between the theme switcher and body if there are no headings to generate a table of contents with. The contents just get a bottom margin which is invisible with more columns.