-Try pasting your CSS code into W3C's CSS validator (www.w3c.org)
-Are you using Windows / Notepad while editing your CSS file? Make sure there aren't any special characeters in the file (use Notepad++ for Windows or use any *nix machine)
-Is your CSS being compiled/packed with eZJSCore?
-If your have CSS in the template file, remember to use {literal}{/literal} tags or {ldelim}{rdelim}
-Make sure there's no comment blocks in CSS messing you up.
I don't understand what you mean by -Is your CSS being compiled/packed with eZJSCore?
My editor is Eclipse
My css was validate with http://jigsaw.w3.org/css-validator and there is no comment in my css file
I'll try to put my style with {literal}{/literal} tags
Thanks again for your help
Véronique
If you take a look at your page source real quick: if there is only one file with a hash-type looking filename like: jkldfsgjklfgf90200ds98090d890fds.css being included on your page, all the CSS is probably being packed with the eZJSCore packer.
Take a look at the ezjscore extension which should be available in at least eZP 4.3+. Its settings in ezjscore/settings/ezjscore.ini has the ability to disable packing for debugging and non-caching behavioral purposes.