This sample demonstrates the Gantt header template feature. In this sample, custom icons are displayed in the column headers.
The Gantt provides a way to define a custom element in the header element. The columns -> headerTemplate property accepts either string or HTML element`s ID value,
which will be used as the template for the header cell.
In this demo, we have rendered the customized template for all column headers.
More information about the header template can be found in documentation section.