DevTools: [SSP] update style rules of SectionPropertyTreeElements

The style rules of tree elements became outdated after the rule was
edited. This patch adds synchronization for them as well.

BUG=430133
R=vsevik

Review URL: https://codereview.chromium.org/692073003

git-svn-id: svn://svn.chromium.org/blink/trunk@184869 bbb929c8-8fbe-4397-9dbb-9b2b20218538