Hello David,
A possible approach is to add a
Border in your
GridViewHeaderCell style just before the
ContentPresenter.
Another possible approach is to edit the default
GridViewHeaderCell template directly. This would be the better option because you will still have a functioning default behavior like change of color of the
GridViewHeaderCell on
MouseHover. You can check our
Editing Control Templates and
Styling the Column Headers documentation articles.
As a side note I should point out that setting
DataLoadMode="Asyncronous" is generally not recommended as it could lead to some problems. This is an old mode and it is not relevant with our latest version. Please remove it.
Please give the suggested approaches a try and let us know how it goes.
Regards,
Boris Penev
Telerik
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