google custom search

Hi, I have a little problem to integrate google custom search properly to my website. My site is rhcounselling.co.uk and google custom search in in the left sidebar and looks a bit funny. I also had it in the content, in the header and footer, I also tried to integrate it with a plugin but the strange looking result was always the same. I think the problem is with the theme (twenty fifteen) and not with the goolge code because it is working fine on a different, not one of the original wordpress, theme. The code in general is working fine and search results are shown properly, the search box only looks not right. I am relatively new to wordpress and don’t really understand all the code things. So, if someone out there is so kind to help me, please use a normal language.

Thanks.
Mona