ruby on rails with html templates

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CSS

HTML

Ruby

i am making a ruby on rails web application, and before i even started the rails project, i designed the whole thing with html css and java. now, all i need to do is add sign in sign up and post blog stuff. to do that i need to put the website that is already made into a rails project, what changes would need to be made to the html to make it work exactly like it did when it wasnt in the rails application?