MahiPro theme gives you an easy way to add custom CSS styles that override theme default styles. This feature is designed to meet the needs of administrators who would like to add their own CSS to their Drupal website.
Note
Styles created with this feature will render only when your website default theme is MahiPro.
How to add custom CSS
Custom CSS can be added from theme settings page.
Home 
Administration Appearance Appearance settings MahiPro
example.com/admin/appearance/settings/mahipro
Enable custom css option and enter your custom css codes.
You may need to clear cache after adding css codes.
example.com/admin/config/development/performance