透明iFrame：在底层页面的背景上显示文本/内容

I am creating a web/mobile app and I would like to be able to display the contents of page1 (page1 is HTML and contains text buttons sliders, images) in an on page2 with opacity=.5 so that the contents of page1 displays on the background image of page2. The problem is that if I set the background of page1 to transparent, then nothing is displayed (page1 looks like white on white on its own, and shows nothing when displayed over page2). If I set the background of page1 = black, then its content displays over the background of page2, but this creates 50% darkening of the background of page2. I haven't been able to figure this out from other SO pages on iframe backgrounds, which there are a number of.I am creating a web/mobile app and I would like