I’ve noticed in the forums, there are a lot of questions regarding the style sheet of the child theme not affecting the output. Their response is to use the theme options custom css. I don’t like to use it that much because it spits out the css on the page rather than keeping it in a file.
If you look at the source code, you can see that your child theme style.css is very high up on the page before several other style sheets. But there is a neat cure for this. Re-Order.
It’s a little unintuitive at first. Where it says
Reset Scripts and Stylesheets
Do this first after activation – May require up to 10 seconds
Go ahead and click, ignoring the buttons above for scripts. You will be presented with a list of all your styles in the order they are loaded, and all you have to do is find the child style sheet and drag it to the bottom of the list. The hit ‘save new order’ in the blue button.
You might have to do it again after installing other plugins that have their own style sheets.