Reducing Space Above Footer

Hello. I am making a simple website for someone using the Yoko theme, which has worked out okay except for the spacing at the bottom of the pages. The main content and each widgeted section finish with a default grey line – which is fine, however there is then a sizeable gap to the footer area.

See the testing site: https://www.simonredux.com/testing

I wondered if it is possible to remove some of this white space area??

Ideally I would like to keep the widget areas just as they are, but remove the grey lines at the end of each main content section on pages; WELCOME, TESTIMONIALS, CONTACT, while reducing the white space to the footer area. I just want to close it up a bit.

I am pretty clueless about php so any advice would be really welcome!