How to increasy the transparency of the background colour

Hello CatchThemes Team, I wonder if it is possible to increase the transparency of the background colour of [header, footer, widgets and the content] of my site. Being able to do this would be great as it will give my page a fresh and modern look as opposed to the old-fashioned impression it gives now it with the 100% opaque colour covering the background image. Is there a code I can use and copy-paste to change the transperancy to let us say 40%, or is there an option which you will be including in a next upgrade of the Cathc Box Pro theme? Many thanks in advance for your help with this. Sincerely, Nadia