How to put all sections background, transparent in version 2017

The method Nancy points out will work, but it's along the lines of using a stick of dynamite to get rid of a gopher.

HTML elements are transparent by default. If you have a color you want to get rid of in the background, all you should need to do is remove the "background" or "background-color" setting from its css.

Are you asking how to make web page background transparent? 

Edit your CSS code.  Or add this wildcard to the very bottom of your stylesheet(s).

* {
    background-color:transparent !important;
}