Slide out tab SCSS: Redeclared display block placeholder selector in IE7-8.
Prevents details/summary elements from being treated as inline by IE7-8. The :not pseudo-selector's presence in the standard SCSS file causes the entire placeholder selector's outputted rule to be ignored by those browsers.
Merge pull request #3246 from EricDunsworth/v3.0-details-ie-display-block

Slide out tab SCSS: Redeclared display block placeholder selector in IE7-8.