[INTERNAL] sap.m.LightBox: Minor css changes
[INTERNAL] sap.m.LightBox: Minor css changes

Change-Id: Ieecab97fc892dfd2da0c6a8a356eea6751140f8a

cschuff/openui5,olirogers/openui5,olirogers/openui5,cschuff/openui5,SAP/openui5,SQCLabs/openui5,olirogers/openui5,nzamani/openui5,cschuff/openui5,SQCLabs/openui5,nzamani/openui5,SAP/openui5,SAP/openui5,nzamani/openui5,SAP/openui5,SQCLabs/openui5