How to edit CSS styles in my theme?
Please do not edit CSS files. You can overwrite all styles by the admin panel.
1. Go to Theme Settings > Quick Edit (Child theme) > Custom CSS You have an editor with syntax highlighting for easier editing. You can also create child theme and edit style via Wordpress editor.
2. Use developer console and find styles that you want to change. Here you have great tutorial.
3. Paste new styles in Custom CSS field. Every main CSS rule can be adjusted. Whenever you want to change theme style always use this field. When you do that you'll have assurance that whenever you upgrade the theme, your code will stay untouched. Avoid making changes to "style.css" file directly. Whenever you change something, you can always export your data using Advanced > Import/Export.