containerCss backgroundColor: 'transparent'

var containerCSS = { ... backgroundColor: this.opt.backgroundColor || 'transparent' }; white backgroundColor of containerCss overwrites the background of html2canvas. changed to transparent and also add an option to set backgroundColor from opt of jsPDF.

Author: kakugiki

src/modules/html.js

@@ -246,7 +246,7 @@
  right: 0,
  top: 0,
  margin: "auto",
- backgroundColor: "white"
+ backgroundColor: this.opt.backgroundColor || "transparent"
  }; // Set the overlay to hidden (could be changed in the future to provide a print preview).
 
  var source = cloneNode(