`test_diag_severity_tokens_route_through_host_theme_tokens` matched the CSS
text byte-for-byte including the alignment padding (`warning: var(`), so a
reformat that keeps the computed value failed it (probe: single-space the
three declarations -> red) while it still could not distinguish which
token/fallback each rung used beyond that exact substring. Parse the
`--hermes-diag-*: var(--color-*, #hex);` declarations with a regex and assert
on the captured token/fallback pairs; a wrong fallback colour still fails.
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