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To do this you will need to work with the external templates for the Download List. By default Sitefinity controls are using embedded templates, however you can download an archive of all control templates from the downloads section on Sitefinity.com, and add them to your site. Then you can choose the controls you want to modify the look and feel and make them use your external template. More information on how to work with external templates can be found here: How to map a view to an external template, in Sitefinity 3.6 or later?
Then after you have the external templates you will need to modify the following file - ~/Sitefinity/Admin/ControlTemplates/Libraries/Modes/DownloadList.ascx
. My suggestion would be to define an AlternatingItemTemplate
besides the ItemTemplate. In the alternating item template you will have the same field, however you will apply different styles. Then all you have to do is to tell your download list control to use the modified control template, see attached image.
All the best,
the Telerik team