In the current version of RadControls it is not possible to modify the appearance of the tooltips, except for their background color. Nevertheless, I have logged this idea in our feedback portal here
, so that you can monitor, comment and vote on it, in order to raise it priority.
For the time being you can manually change the border width and the padding of the tooltips by getting the class of the tooltip wrapper and change its CSS. For example:
/*Modify the border width*/
/*Modify the padding*/
Regarding the tooltips that come from the RadTooltip and the ones that come from the RadHtmlChart, they are not the same, so I am not sure if you can directly use the RadTooltip upon the RadHtmlChart.
I have also updated your Telerik points for sharing your ideas with us.
the Telerik team
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