To change the background color of a region assign a static ID to the region and add CSS-styles in top of the page.
To color the background with a certain opacity without effect on foreground text use this code:
<style>
#Tmp1{
background: rgba(200, 54, 54, 0.5);
}
}
</style>
The region(s) with the static ID Tmp1 are effected.
The following code is also possible, but then the opacity of the text is also set.
<style>
#Tmp1{
background-color: red; opacity:0.5;
}
}
</style>