CSS for background

Can someone help. I want to change the backround colour of the FB comments section to white. I tried changing to the light skin but that didn’t work. My page background is black but I want the Heateor FB comment white.

I tried this in custom CSS but it did not work
.pluginSkinDark, .pluginSkinDark .fcb {
color: #333 !important;
background-color: #fff !important;
}

Any ideas?

Thank you.