Describe the bug
The CSS Lint CI check is failing on public/css/calendar.css with 26 errors related to vendor-prefixed properties such as -ms-flexbox, -webkit-box-shadow, and -webkit-user-select. This is affecting all CI runs on the main branch and all open PRs.

Expected behavior
CSS Lint CI check should pass on the main branch.

To Reproduce

1. Check any CI run on the main branch after March 26, 12:35 PM PDT
2. Open the CSS Lint check
3. See 26 errors in public/css/calendar.css

Additional context
The errors appear to have been introduced by PR #12564. The last passing CSS Lint run on main was CI run 8514 (March 26, 12:20 PM PDT). All runs after that fail. The error output indicates 22 of the 26 errors are auto-fixable with the --fix option.