Hello, @Maheeb Sons,
1.. I have checked the link that you provide on mobile all categories appear fine see image: https://postimg.cc/RqfMG7NJ there is no issue. please check back to your site after clearing the browser cache.
2.. Sorry to say, that you cannot control the speed of the mega menu from the theme options or with the help of custom CSS code it requires additional customization.
3.. You have to set the border-bottom on the menu items to set the verticle line like I did please check the image: https://postimg.cc/t12zKnJh
Regards 8Themes Team.