Wordpress: How to Change CSS for Color, Background-Color and Font-Family

Hello,

I have the h5p plugin running in an wordpress installation.

The Requirement is:

• The h5p-plugin and the content-type H5P Couse-Presentation shall have the same color, background-color, and font-familiy as the page where the h5p content is placed.

Question: How do I do this?

• Apply changes via my Wordpress-Theme? (I use a child-theme)
• Apply changes via an own wordpress-plugin?
• Or just with an own piece of JavaScript with jQuery to change CSS-Properties?
• The h5p-content is rendered in an iframe.

Thank you for your answers in advance.

Yours

Thomas