Changing font and colour of widgets in sidebar

Hi, I am trying to change the colours and fonts of the sidebar widget to match my theme.

I would like the font to be Montserrat and the font colour to be #13556a – if I could change the button too that would also be excellent!

I have searched on the forums and tried all the CSS code suggested but it’s just not working for me. I would love some help – it looks so weird on the page right now!

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