@nadlurinadluri, you can
<html><panel> with a menu created the way you want using html and static image files.
2) You can save the same as a pre-built panel.
3) Hide Splunk's App bar
4) Use prebuilt panel for applying your menu in each dashboard.
Following is one of my older answer on similar lines: https://answers.splunk.com/answers/595047/can-we-implement-cascading-dropdowns-in-a-dashboar.html
Hi @ nadlurinadluri
you can create a static folder in apps folder of the app and put the images there.
check your $splunkhome$/etc/apps/search/static/ folder to have an idea of what file images need to placed.