Hey there Osteopat,
Hope you’re well today!
This should be possible with some custom CSS. Could you please try adding the following CSS code in the style.css file of your child theme or add it in your site using the following plugin:
https://www.ads-software.com/plugins/simple-custom-css
#secondary, .site-header, .site:before, .site-footer {
background: #000;
}
Replace the color hex value with the color of your choice. You can use sites similar to this one to get hex value for the color of your choice:
https://www.color-hex.com/
Hope this helps ??
Best regards,
Bojan