Creating a Child Theme

I would like to add a ribbon to my website and understand that a child theme is optimal for adding any html code without the potential of it being overwritten by an update. I have gone over the steps presented HERE and in Step 4, it states to download both the modified stle.css and original style.css. My question is: Where do you find them both? I have already gone into the public_html/wp-content/themes/oceanwp and downloaded the style.css file there, but is this the “modified style.css” or the “original style.css” and where can I find the other? Thank you