Hi Rama Teja,
You can add your own custom css classes in custom.scss files and call it in your pages.
Your can follow this link for more reference : https://docs.mendix.com/howto/front-end/customize-styling-new
Hi Rama Teja,
To open your Mendix project directory from Studio Pro, click “Project” in the top menu-bar, then click “Show Project Directory in Explorer”.
select the theme folder→ and select styles folder → and select web folder→ and select sass folder
→ open app folder → custom.scss file start your stylish effects for front end
for reference
https://docs.mendix.com/howto/front-end/
https://docs.mendix.com/howto/front-end/customize-styling-new#file-and-folder