fix: treat at-rule names as case-insensitive across rules

[thecalamiity]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Ensure at-rule names are treated case-insensitively across rules, aligning with CSS syntax and preventing missed detections when authors use mixed-case at-rules.

What changes did you make? (Give an overview)

• Updated rule listeners to use case-insensitive matching
• Added mixed-case variants to tests to verify case-insensitive behavior

Related Issues

Is there anything you'd like reviewers to focus on?

[snitin315]

Can you also share the official reference where it is mentioned these are case insensitive?

[thecalamiity]

The at-rules affected in this PR are defined across different specs, so I’ll need to track down the relevant references. In the meantime, here’s a StackBlitz reproduction for @import.

[nzakas]

CSS at-rules are case sensitive, so closing.

[thecalamiity]

@nzakas CSS at-rule names are case-insensitive. I tested each at-rule changed in this PR to confirm this before opening it.

Here is a StackBlitz reproduction for @import

[nzakas]

@thecalamiity it appears you are correct. I had to dig deep into the spec to find this:

Tokens match if their value is a match for the value defined in the grammar. Unless otherwise specified, all matches are ASCII case-insensitive.

In the future, keep in mind that simple repros in a single browser don't mean much -- browsers can implement things different ways. What is more useful is finding the text in the specification that backs up your claim.

[nzakas]

LGTM. Would like @snitin315 to review before merging.