When using the Grid with the Material skin, the drag selection overlay is not visible. After inspecting the DOM, I found that the overlay element uses the GridRowSelector_Material class:

<span class="GridRowSelector_Material" style="position: absolute; z-index: 1000100; opacity: 0.1; top: 525px; left: 321px; width: 844px; height: 36px;"></span>

However, this class is not defined in the Material skin's stylesheet, which results in the overlay having no visible background.

1. Use the Material skin with a Grid that has drag row selection enabled - https://demos.telerik.com/aspnet-ajax/grid/examples/functionality/selecting/row-selection/defaultcs.aspx?skin=Material
2. Select multiple rows using click-and-drag.
3. Inspect the DOM - the span element for the overlay is rendered, but has no effective styling.