Inject custom css only when kWidget is available and only if a custom css is defined by the theme plugin. (#2981)
Inject custom css only when kWidget is available and only if a custom css is defined by the theme plugin. (#2981)

SUP-8883
omridevk/mwEmbed,kaltura/mwEmbed,bordar/mwEmbed,slash851/mwEmbed,kaltura/mwEmbed,slash851/mwEmbed,FlixMaster/mwEmbed,kaltura/mwEmbed,FlixMaster/mwEmbed,tanyaLibatter/mwEmbed,panda-os/mwEmbed,panda-os/mwEmbed,tanyaLibatter/mwEmbed,kaltura/mwEmbed,alexmilk/mwEmbed,FlixMaster/mwEmbed,alexmilk/mwEmbed,slash851/mwEmbed,omridevk/mwEmbed,bordar/mwEmbed,tanyaLibatter/mwEmbed,omridevk/mwEmbed,panda-os/mwEmbed,tanyaLibatter/mwEmbed,bordar/mwEmbed,panda-os/mwEmbed,slash851/mwEmbed,alexmilk/mwEmbed,FlixMaster/mwEmbed,bordar/mwEmbed,alexmilk/mwEmbed,omridevk/mwEmbed