I have one and I'm going to share it with you.
A style guide is a simple page that has details of:
the fonts you use,
colours (and their numbers in HEX and RGB so you can use them on different platforms),
key messages and for me,
I've included a word cloud from my website (shows key words I use the most)
and a mood board of some of my social media posts.
So, here is my present to you
And here are some cool tools to use: