Custom css for part of page

I found a template online for content blocks with nice hover effects which I want to add to just one part of a page of my website. However, when I paste the css from the template into the page between <style></style>, it doesn’t apply to the html. I guess it’s due to the php templates, but I am not really familiar with php.

So: how can I make it so that the part of the page is affected by the css?

P.S.: Here is the link to the hover effect which I am trying to achieve: https://tympanus.net/Development/HoverEffectIdeas/