You need to add the current CSS styling you have in the style element in your HTML into the styles.css editor. In essence, you are duplicating the CSS, you will have it in both the index.html editor and the styles.css editor.
Do you know how to access the styles.css editor? Do you know where to find the current CSS in the styles tag in your HTML. Do you know how to copy/paste that CSS from the HTML into the styles.css editor? I’m asking all of these questions because I don’t know what you don’t understand. Please be very specific.
Can you use google translate to read this in your native language? You can also type in here with your native language and we can use google translate to read it. Do what it easiest for you.