Dashboard with theme toggle, HTML, JS, SASS, BEM, Flexbox, CSS Grid

I probably spent more time than I should tinkering with this one. These helped me get things done the way I wanted:

• https://www.bram.us/2020/04/26/the-quest-for-the-perfect-dark-mode-using-vanilla-javascript/
• https://codepen.io/alvarotrigo/pen/WNXLZNN

I made changes to the original code but most of the heavy lifting was already done. What I'd like you to tell me is:

• How you would improve on the JS (splitting the code into smaller functions?)
• How the CSS could be improved in your opinion. I reached for multiple things at once and I guess the readability might have suffered for it.