The dotted separator wasn't displaying because the height of the
separator was too small. This change overrides the height for the dotted
separator only.
* Remove empty CSS selectors.
* Fix RTL styles for large quote blocks.
* Remove incorrect file button hover styles.
* Add overflow auto to preformatted and code blocks.
* Correct centred styles for widgets.
* Increase font size of comment widget.
* Remove margins from recent posts widget when displayed as grid.
* In themes RTL styles, remove border from block quote.
* Update separator styles so the front-end and back-end match
* Update table styles in the editor to match the front-end
* Update code styles in the editor to match the front-end
