WordPress Plugin UI Customisation

Hi folks,

I am working on a client’s WordPress site, on which they have used Bullhorn WordPress Plugin.

They would like to update the UI of the careers page to follow brand colours etc, however I have been unable to do so by adding custom CSS.

My question would then be: are there any ways to customise the look and feel of the UI, other than editing the core CSS file of the plugin?

The page I need help with: [log in to see the link]