Well - after the fifth try at doing exactly the same thing it works, deleting cache, retarting my Internet browser. Go figure.
I tmpl folder into my main template, renaming it jw_all videos and modified the following, removing padding, radius, and setting background color to white. Don't know why it wouldn't work before but does now.
.avPlayerWrapper { display:block; text-align:center; clear:both; }
.avPlayerWrapper .avPlayerContainer {
display:block; padding:0px; margin:4px auto;
-webkit-border-radius:0px; -moz-border-radius:0px; border-radius:0px;
-moz-background-clip:padding; -webkit-background-clip:padding-box; background-clip:padding-box;
background-color:#ffffff;