there is opacity parameter with typo – when you change the value of opacity in admin (previous post) to 3%, in CSS there is opacity: 0,03, should be 0.03 (with dot instead comma).
In my case – there is problem with OPACITY settings in Customise -> Colors -> Header, down. Changing opacity to 0% – header image is vievable. Changing to 1% or 10% or 50% – image is covered by Overlay permanently.