I do know nothing about unity. But your scale game does not scale. At all. The play screen in the middle stays the same size, no matter how I size and zoom my browser. Even with full screen it still does not scale. Only now, in fullscreen, the non scaled item is still the same size, while the surroundings did get scaled, despite the fullscreen setting. It should both (background and start box) adjust in size while zooming the browser and stay the "fullscreen" size while fullscreen no matter the zoom.
Make the game fullscreen, after zooming your browser in or out. Even better, go to fullscreen and then press ctrl+/-.
This is not how scaling is supposed to look. But that is the reason for the thread, I gather ;-)
My guess would be, you tell the engine somethin has to be a certain fixed size in a context where it should be adjustable (scaleable). So maybe you do give instructions not for the virtual screen that can be adjusted, but directly in absolute terms. Similar to when you give pixel values instead of relative values in css. That looks awful in a non adjust high res screen and is the reason people user their windows in 300% default zoom for that resolution, instead of benefitting from the high resolution. Even old full hd is default 150% zoom. So my virtual pixel resolution the browser tells the site is much smaller than my screen could handle.
If I type window.screen.width in the javascript console, it resolves to 1280 and not my screen width.
Scaling and sizing is awful. My sympathies.