I want my survey page to look like the example on freecodecamp

I want to make my project have a similar transparent background like the one here https://codepen.io/freeCodeCamp/full/VPaoNP. and yes, mine has not come close to it at all https://codepen.io/Aqua7/pen/zYqxgMr

You could glance through the source code to get a feeling for how they made it. But the idea to use the background properties: background-attachment, background-color, background-position, background-size, and background-image with some gradients. This topic now similar to this Creating double background in survey form