How to select multiple elements that are children of given element?

I have <div id='mydiv'> and I need to select all pre and div elements that are children of #mydiv.

I could do it this way:

div#mydiv > pre, div#mydiv > div

but, can it be done so that #mydiv is referenced only once?

div#mydiv > pre, div

will select all divs on the page regardless if they're children of #mydiv, so the comma isn't a way to do it. Maybe there's another kind of syntax I don't know about?

You'll have to reference #mydiv twice...

#mydiv > pre, #mydiv > div

I removed the extraneous div element selector as the ID is specific enough.

As far as I know, there is no shorthand for selector grouping.

See "Selector Grouping".

Although, with LESS, it is possible in the "Nested Rules" section.

The only way to reference the id only once is to use it with the * selector:

#mydiv > * {

which will apply to all elements that are children of that div.

Depending on what styles you plan to apply this might be workable (I typically use this to zero-out margins, padding and border styles), but it's still probably best to do it the first way because it makes it easier to make exceptions/changes later down the road.

You can actually group selectors with :is().

So in your case you would use it like this:

div#mydiv > :is(pre, div) {
     // CSS
}

Here is the documentation https://developer.mozilla.org/en-US/docs/Web/CSS/:is