This is to bring in your knowledge that top bar in the theme can be made floating on desktop but when we see the website on mobile platform the top bar is static and one scrolling downward it is not accessible until we scroll back ward or use the move to top button. Need modification in the theme get it fixed. I am using NIRVANA for my website.
Mobile devices have a limited viewing space. Keeping elements fixed on the screen while scrolling would diminish this space further. It is a design choice to disable the fixed status of the topbar on smaller devices.