Fix laptop overlay

This MR fixes #12 (closed), needs to be merged with aether-sass!40 (merged)

By removing the rem based margins on the screenshots and dropping the margins on the image itself, it is easier to position the screenshots on the laptop consistently.

All the manual fixes in the announcement pages as well as on the plasma page have been removed.

The MR also adds a light inset box-shadow to give the screen a bit more depth.

Left is before:

Mobile: