CSS fixes for details/summary polyfills and alerts

These fixes normalize a lot of the styling between native and polyfill implementations of details/summary elements.

It also improves the layout of alerts when combined with details/summary.

Plus, some RTL enhancements.
Oops, yeah, the line changed with my amended commit.
https://github.com/Pacoup/wet-boew/blob/alert-css-fixes/src/base/bootstrap-overrides/_base.scss#L762