how to change the sidebar headings in the Spine theme

I had a question via email asking how to make the sidebar headings smaller, and I thought it was worth posting for everyone who might have the same question. So here’s how.
I think the best way would be to create a child theme and add the following code to the functions.php file

How to create a child theme

You could also possible use CSS, again in a child theme or with the custom CSS Jetpack feature