This WordPress live chat plugin can be adjusted to match the style of your website. Choose its position on a webpage: left- or right-side tab or button; apply your website’s color theme or pick the colors, fonts, and animation from the gallery.
I was able to plug this in and have it up and running in just a few moments. No tricky API key, no coding at all. They even dynamically import all of your color settings so that the popups are easy to customize. Very impressed and highly recommended!