Blog > Article > background

Hello,

I would like to have a specific background color for my blog articles only (background: #e9e9e9) and keep my background color for others pages (background: #ffffff).

I try this but it does not work :

body.postid .contentclass {background: #e9e9e9 !important;}

How can I do it please, without to do specific for each article like this : body.postid-XXX ?

Thanks for your help