#1. You must sign in to the website and navigate to the appropriate [product detail page] page. You must choose "HTML / CSS Editor" from the "site" main navigation bar.

#2. You may see the editor popup after clicking. You must choose "Edit HTML anyway" in order for the editor to open. The detail page's HTML code is visible.

#3.Choose "SCSS" from the "XML HTML" dropdown menu. You can write CSS or SCSS inheriting from the parent specific class.[If  you don't have any specific class in that html page, you can add it custom using Html page code]. Writing CSS with a specific class name allows the design work to be done on the page by itself.