Set picard background to be lightgray
Set picard background to be lightgray

It's a dark gray by default since it pick up
the EosWindow styling from the SDK theme. The dark
color makes it difficult to see box shadows, so
let's make it lighter.

https://phabricator.endlessm.com/T15903

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib