Layer order is fixed by the first place each layer name appears in document order. A host's stylesheet
that writes @layer sxl-overrides { … } usually sits in <head> ahead of anything a component renders,
which would make sxl-overrides the lowest layer. Placing the statement before every other sheet keeps
sxl-defaults < sxl-app < sxl-overrides however the host's sheets are ordered.
Puts the
sxl-*cascade-layer order statement first inroot(the document's<head>, or a shadow root), once per root.