Opacity troubles main block and header image

I was wondering if someone could point me into the right direction.

I have changed the opacity of the main block as shown below:

/* =Structure
————————————————————– */

/* The main theme structure */
#access .menu-header,
div.menu,
#colophon,
#branding,
#main,
#wrapper {
margin: 0 auto;
width: 940px;
opacity: 0.9; <——-
}

Which works more or less as intended except I would like it not to affect the header image or widget images.

Can anyone assist?

Or even better, have everything transparent apart from images, widgets and post blocks (the text)?

Thank you in advance!
S

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