Merge pull request #8970 from ahocevar/zindex

Fix zIndex positioning

src/ol/renderer/Composite.js

@@ -31,6 +31,8 @@ class CompositeMapRenderer extends MapRenderer {
     const style = this.element_.style;
     style.width = '100%';
     style.height = '100%';
+    style.position = 'relative';
+    style.zIndex = '0';
 
     this.element_.className = CLASS_UNSELECTABLE + ' ol-layers';