SMapp

I have little understanding of what I just did, but it worked. So thank you.
For the benefit of others, here is exactly what I did:

Install the Simple Custom CSS plugin. (I was cautious about using Jetpack as I get the impression you loose some privacy by connecting it to wordpress. You get nothing for nothing, but Simple Custom CSS doesn’t ask for account name and password, which I prefer.)
Activate plugin
Go to the plugin’s settings It gives you a pane to enter the code in.
Copy and paste the code from above into the pane
Click on Update Custom CSS button bellow the pane.
And that’s it.

Thanks.
Didn’t know you could do that. Sorry!