How to minimize the space between sidebar and content

I see - how wide do you want it?

You could adjust the media queries widths.

Here are the standard breakpoints https://www.w3schools.com/howto/howto_css_media_query_breakpoints.asp

anvil has set their break point to

@media(max-width:991px)/@media(min-width:992px)

If you change the media queries to be the next break point up

@media(max-width:1199px)/@media(min-width:1200px)

Then it should work for extra large devices rather than large devices

… maybe