wp-includes/js/tinymce/plugins/media/css/content.css

   1 .mceItemFlash, .mceItemShockWave, .mceItemQuickTime, .mceItemWindowsMedia, .mceItemRealMedia {border:1px dotted #cc0000; background-position:center; background-repeat:no-repeat; background-color:#ffffcc;}
   2 .mceItemShockWave {background-image: url(../img/shockwave.gif);}
   3 .mceItemFlash {background-image:url(../img/flash.gif);}
   4 .mceItemQuickTime {background-image:url(../img/quicktime.gif);}
   5 .mceItemWindowsMedia {background-image:url(../img/windowsmedia.gif);}
   6 .mceItemRealMedia {background-image:url(../img/realmedia.gif);}