This is what I have in my project CSS to deal with a similar issue, though I find different issues on each project depending on what I do with the general CSS & columns in particular:
/* Fix TinyMCE gremlins */
#internallinkcontainer div.row {
/* Image browser was jumbled */
float: none;
}
#content #internallinkcontainer .list.item span,
#content #internallinkcontainer .list.item a {
/* Link browser was packed too much */
position: inherit;
}
#internallinkcontainer input[type="radio"] {
vertical-align: middle;
}
/* @end */
Which get's my Link Browser looking like this again:
Apart from the Diazo-CSS troubles, it sounds like you might be having trouble with
plone.css getting cached. The following is from the developer manual with amendments by myself that have not yet been pulled in.
plone.css
plone.css is automagically generated dynamically based on the full portal_css registry configuration. It is used in e.g. TinyMCE to load all CSS styles into the TinyMCE in a single pass. It is not used on the normal Plone pages.
plone.css generation:
https://github.com/plone/Products.CMFPlone/blob/master/Products/CMFPlone/skins/plone_scripts/plone.css.py
Note: plone.css is @import-ed by dialog.css which "hides" it from a browser refresh of a normal Plone page, even when Plone is in development mode. This means you may find you do not see your CSS updates within the TinyMCE plugin (e.g. in the link/image browser) whilst developing your theme. If this is the case, then simply do a hard refresh in your browser directly on: /plone.css to clear the cached version.