In your css file, you describe and html element h1. In your hype file, you give a class of h1 to an element div.
Add a . before h1 in your css file, like that: .h1 and it will be a class instead of a html element. It should solve your issue.
Or to avoid mixing html elements and class, replace h1 by title-large for example.
And don’t forget your css basics: html element description without anything (h1, p, em, stuff like that), a dot . before a class name, and a # before an id name.