Thanks for using Syncfusion product.
We have analyzed this. The range navigator can be made responsive on resizing the web page by enabling the below property
On enabling this the size of the range navigator is set based on the size of the web page. So on resizing the web page, range navigator is fit to it.
And in addition the below property is used to make chart as responsive
We have also made a sample to illustrate this for your reference. Find it from the below location
Please let us know if you have any concern.