Better calculation of centering button

git-svn-id: https://plugins.svn.wordpress.org/cookie-banner/trunk@844426 b8457f37-d9ea-0310-8a92-e5e31aec5664
Further CSS updates

git-svn-id: https://plugins.svn.wordpress.org/cookie-banner/trunk@844427 b8457f37-d9ea-0310-8a92-e5e31aec5664