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bug: Invalid @supports syntax in icon.css breaks under strict CSS parsers (e.g. Lightning CSS)

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Assessment

Difficulty
1/5
Estimated time
Under an hour
Newbie friendliness
92/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
css
Domain
frontend

Research direction

Open icon.css and locate the @supports rule shown in the issue. Update its condition to use the explicit grouping described in Expected Behavior, then run the Lightning CSS reproduction or swap in stencil/core 5.0.0-alpha.35 and run npm run build to confirm the stylesheet parses successfully.

Written by the indexing model from the issue text.

Description

triage
Current Behavior

icon.css has:

@supports not selector(:dir(rtl)) and selector(:host-context([dir='rtl'])) {
  :host(.icon-rtl) .icon-inner {
    transform: scaleX(-1);
  }
}

Per the CSS Conditional Rules spec, not and and can't be mixed in a <supports-condition> without explicit parens grouping each operand.

Whilst PostCSS allowed this formatting, Lightning CSS (used in the upcoming stencil v5 release) fails with: Unexpected token Ident("and")

Expected Behavior
@supports (not selector(:dir(rtl))) and (selector(:host-context([dir='rtl']))) {
Steps to Reproduce
const { transform } = require('lightningcss');
transform({
  filename: 'icon.css',
  code: Buffer.from(`
    @supports not selector(:dir(rtl)) and selector(:host-context([dir='rtl'])) {
      a { color: red; }
    }
  `),
});
// throws: Unexpected token Ident("and")

Alternatively, swap in stencil/core 5.0.0-alpha.35 in the main ionic repo and run npm run build

Code Reproduction URL

No response

Additional Information

No response

Dominant language
TypeScript
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