usvg's style sheets (simplecss) drop rules whose selector has a :not(), so
rect:not(.keep) { fill: green } left the rect as it was. The text pass's own
cascade now reads :not() of a list of compound selectors (counted as its most
specific argument), and the import pre-pass writes what such rules set on an
element into its style attribute, with the value that wins the cascade there,
so usvg reads what CSS would: against other rules, the style attribute and
!important, inherited from groups, display: none and CSS transforms included.
Selector lists are split at top-level commas only.