Responsive design with plain html and css

The elements where I've used an absolute position (e.g. the man's avatar and the purple rectangle with the text) are rendering differently (with broken offsets) in my smartphone. However they show up fine in the browser even when I change the size. I need to dig a bit more into this.

Also, could not find a way to crop the green helix in the background. If you make the window big enough you will see them rendering out of the webpage.

This was a decent sized project! I'm happy with the result though, feedback is more than welcome!