Query on slide & banner overlays

Hi

I’m just wondering if there are any color overlay options for slides or promo banners?

The problem I’m looking to solve is white text on a slide or a banner that is hard to read over the original image. I’d like to darken the background image to my taste so the text stands out more. I don’t see any options for this and there may not be – is there any CSS I can apply to achieve the goal?

I know that I can darken the images in photoshop before uploading – but I’d prefer a better solution through element settings or CSS.

See the example at the link below – I’ve darkened the slider images at the top of the page in photoshop. The promo banner further down (Interested in selling Ark Farm Innovation Products?) hasn’t been updated and it is very hard to read the white text.

Login details in private content if required

Thanks