what and where are they, these gray bars in the sidebars?

Hello everyone,

i am trying to customize my bullet list and already found a very helpful thread on it. But what are these gray bars (changing black on hover) in the sidebars and where do I go to replace/delete/color/modify them? Is it CSS-->Insert? which code to insert?
thanks much,
PS. my URL is frenchtasticpeople.com
Herman