You should probably use specificity first, then important, just in case you need to over-ride it in the future.
> Note: Repeated occurrences of the same simple selector are allowed and do increase specificity.
*:is(#a#b, .someclass) {...}
overrides any selector with a single id; you add more ids to override more specific selectors (except inline stiles and !important)
If you really have to select that element by ID for some reason, you can use an attribute selector instead—`[id=foo]`—and then it’s also in bucket B and can be controlled in the normal way.
Basically, you should consider ID selectors (and element selectors) an antipattern and never use them.
Edit: Take this example:
div {font-size: 60% !important;}
If I can't control the order the CSS is loaded, and I can't change that line directly, how do I modify it? Like this: html div {font-size: 70% !important;}
The use of !important isn't some simple way of bypassing ever-increasing specificity. In many cases it just makes things more complex.