added new modal background color
added new modal background color

blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-portal,blockstack/blockstack-portal