There is a similar question in: Google App Script background transparent with HtmlService with no satisfactory answer.
In my situation, I have this simple Apps Script embedded in Google Sites:
CODE.GS
function doGet() {
return HtmlService.createTemplateFromFile('Page')
.evaluate().setSandboxMode(HtmlService.SandboxMode.NATIVE);
}
PAGE.HTML
<html>
<body style="background-color:transparent">
How do I make it<br/>transparent ?
</body>
</html>
resulting in a page that looks like this:
https://sites.google.com/site/seanpj01/backtest
Even if the trick of setting
<body style="background-color:transparent">
works if implemented as a straight XML-wrapped gadget, it fails in this situation (I suspect CAJA). There is a discussion on this problem here: http://productforums.google.com/forum/#!topic/sites/KU9nSz37c6U
but again, to no avail. Thanks