fix css selector for canvas element in 3d dfg-viewer

only select canvas in 3D DFG-Viewer instead of gloabal

Resources/Public/Css/3DViewer/main.css

@@ -36,7 +36,7 @@ a.wisski-inline-iip > div#wisski-iip-cont > img {
     visibility: hidden;
 }
 
-canvas {
+.tx-dlf-view-3d canvas {
     display: block;
     z-index: 0;
     position: absolute;