TwentyFourteen Make Contant-background and Sibear Semi-transparent

Hi how do I make the twentyfourteen theme give me a transparent content-background (not transparent content), and also do the same for the side bar. basicaly I want to have a colorful grpahic background that can be seen behind everything.

I tried this:

/*You can make a transparent background color only for CONTENT background by using rgba color value in CSS rather than using opacity.
RGBA stands for Red, Green, Blue, Alpha Channel.
The first step. You have to find the id or class CSS selector of your content background element.
If your content background is declared as <div class=”content”> then in your style.css, try to do this :
It’ll make the background color has opacity 70%, but the contents inside (text and images) are still at 100%.*/

div.page{
background-color: rgba(0.7, 0.7, 0.7, 0.7);
/* rgb = 0 0 0 is black color */
/* a = 0.7 is 70% of alpha channel */
}

and even changed the div ID to “main-content” and again to “page”, but it didn’t work.

This is what I want:

It’ll make the background color has opacity 70%, but the contents inside (text and images) are still at 100%.