Hello Kirti,

You could look in the browser in the HTML what class is of the object you want to change the color of. See example:

Then you can customize the styling. The documentation, https://docs.mendix.com/howto/front-end/customize-styling-new/,  can help you with that. There also is a great learning path for it: https://academy.mendix.com/link/paths/105/Style-your-App-with-CSS