Hello,
This issue is most probably caused by your CSS styles definitions for the live site. They are actually being applied in the Design mode as well so they might interferee with some
CMS Desk styles. You need to use tools like Firebug to identify which styles need to be adjusted and then you can override their definitions using the ~App_Themes\Default\DesignMode.css CSS stylesheet. Since this stylesheet is loaded after the live site one, CSS class definitions will be used with higher priority. Alternatively, you can use also the
!important directive in this DesignMode.css stylesheet.
Hope this sheds some light.
Best regards
Ondrej Vasil