Solution for this topic

Hi Sophie,

I hope you are well today and thank you for your question.

You can achieve it by adding the following CSS code in the Custom CSS code option of your theme on the below path.

Admin Area -> Appearance -> Theme Settings -> Custom Code -> CSS Code

.sh-single-image-overlay {
    background-color: rgba(0, 144, 243, 0.8);
}

Best regards,
Shufflehound team