content area semitransparent

hello,

I would like to modify 'rooms' template (joomla 3) in the following way:
the content area should appear semitransparent above the custom picture background (which spans from side to side of the screen)
The top menue should be 100% transparent. The appearance should look like a semitransparent piece of drawing paper presenting the content (see sample pic) I think I have to change the colorcode 'ffffff to rgba (256, 256, 256, 0.4) but i can't find the appropriate template file.

Hi there,
Template customizing is not regular template support:
We are committed to help you with any type of support query, however we can't provide extensive help in terms of customizations. In general customizations may look simple but you will require solid knowledge of web technologies and programming skills to do them or hire a professional who can do it for you.

Add this code to your file: css/custom.css

.uk-container,
.tm-content {
background: rgba (256, 256, 256, 0.4) !important;
}

How to customize a template:
www.joomlaplates.com/template-customizing