I would like to get THIS kind of result
After you enter the text, apply to it the Normal style (from the dropdown in the editor toolbar) and then assign the background color. The Normal style puts your text in a p tag which is by default width:100%, and the background-color rule is then added to this tag resulting in the desired effect.
I tried your advice but it does not work . I am using IE8. Is there anything which must be set to get 100% width?
I try now and....it works!!! Thanks a lot! I don't have to type HTML <div> anymore! What a relief and a gain of time!