I already replied to the same question in your other thread, however I am pasting my reply here too:
Generally speaking you could make changes in the CSS files, however the change you mentioned (changing background color of .k-chart .k-mask) is not visible because .k-mask is used in Kendo UI StockChart (while in the provided configuration you use Kendo UI Chart). In order to assist you best and provide concrete recommendations I would like to ask you to provide more detailed information about the exact component from the Chart you would like to change. Thank you in advance for your cooperation.
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