Once stylesheets were inlined, the editor's default CSS parser read
them through the browser CSSOM, where a shorthand that contains var()
(background: var(--surface-1), border: 1px solid var(--border)) comes
back as empty longhands. Every card, panel and border on an imported
page vanished, leaving text on a flat dark background. The official
PostCSS parser plugin keeps those declarations intact; vendored like
the rest, no CDN.
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