In the module setup interface and menu item settings interface there are "module class suffix" "Custom module Name CSS Class" and "menu item link CSS class" "target page CSS class" such as:
The CSS class referred to here refers to the class selector of CSS, which allows us to add additional classes to the modules and menus without modifying the source file, so that we have the flexibility to control the style of the Web page.
This allows us to use. Red or. well.red in the CSS file to define the style for the login module separately. Many Joomla business templates have many built-in styles that allow users to activate by adding a preset class.
However, it is important to note that you may need to add spaces in front of the class, because different template developers may have different ways of handling it, just need to see the page generated by the class to know if you need to add a space, after all, well red and wellred are completely different.
Joomla CSS class suffix