User blog comment:DaNASCAT/Technical Update: March 17, 2015/@comment-1251315-20150318113811/@comment-126761-20150318164338

I should note: the new CSS/JS/Lua editor style is not quite the same as what is on Special:CSS - we're looking to phase out Special:CSS's special layout (with its annoying scrollbars), and convert it to the new CSS/JS/Lua style.

The special search box does have additional features over the basic browser search (at least, unless you use browser extensions), though.

I'm not reproducing the second issue you mention, though (in CSS/JS/Lua or Special:CSS, in Firefox or Chrome) - so I'm not sure what might be going on there.