Hello,
You can make CSS changes in custom.css file or Child theme and after updating the theme, they will not be lost. Here is a video tutorial how to create custom.css: https://www.youtube.com/watch?v=Qok2zRedRMY&feature=youtu.be. Also read more here how to create the Child theme https://codex.wordpress.org/Child_Themes
Regards, Robert Hall.
