You cannot edit this file, since it is dynamically build based on your theme configuration, scss override, ...

If you want alter your style, in edit mode of your website, you can click on the 3th tab 'Theme' and change a lot of settings. If you need to change others things, change scss variable, hardcode css... you can add it with the 'customize > html_editor' , you have the dropdown xml/scss/js, click on scss and add your rules.

KR