How to override Solidres CSS
If you want to modify the CSS of Solidres, you would think about modifying Solidres CSS file which is located in /media/com_solidres/assets/css/main.css, however directly modify that CSS file will make the upgrade of Solidres harder in the future. Fortunately, Joomla provides a great way to override extension’s file.
To override Solidres CSS file create a new folder in your template to store the override CSS file and copy /media/com_solidres/assets/css/main.css into it so that you will have the following structure /templates/your_template_name/css/com_solidres/assets/main.css.
Now Solidres will automatically load CSS from the new override folder instead of the original one.