Change breakpoint for toggleable, sticky mobile sidebars

Hello to the forum and thanks for this excellent free theme.

The option:
Customize -> Main Body -> Sidebars: Design and Mobile Setting -> Sidebars sticky on scroll ? (Decide if your sidebars should be sticky on tablets and smartphones devices.)

…can be activated, but as the breakpoint for toggleable sidebars is 320px it doesnt have an effect. How can I achieve sticky and toggable sidebars on mobile just like on tablet ?
Is there an easy way to change the breakpoint somewhere ?
Can this be achieved else with changing the media-queries only ?