Two CSS grids side by side, one is scrollable, the other isn't
Although this is not a full answer It will shorten your code,
You could remove 'background-size:cover;' &amp; replace it with a class of bGCov,
(As your declaring this multiple times &amp; if your application grows larger With many more Images, this will save many, many lines of code) 
Aswell as Use Bitly URL shortener, to shorten all of your Image URL links, make sure to name them something farely short but related to the actual image as it makes keeping track of them easier later on.
Also if you started using scss background-position and a few other things could be made into variables.
this would shorten you code for a few lines...