These images belong to their respective owners/creators. I simply added transparent black boxes and blur to the areas that have text on them, and minor gradient/hue changes. I'm using 21:9 resolution but it's 16:9 in menu, so this was tested on 1920x1080 only, if you're using other resolutions, the black boxes might not line up with the menus, if too many people get that problem i will release a version without any black boxes, but it will look a bit worse and the text might not be readable in some places.
Installation: Put the folder inside the zip folder to mods/Menu Backgrounds/assets and go to mod options inside payday 2, pick the synthwave preset from the Menu Backgrounds mod options and that's it!