I like the changes but I have one suggestion. There is an option to select all cards or deselect all cards, but is could you add a button to select all cards not in a user-created subsection? I use the EDHRec copy paste feature by choosing all the lands I want in EDHRec, then i copy and paste into the deck using the "paste/upload a decklist", then I create a section for lands and move them all into that section (repeat for ramp, card draw, etc.). Rather than select each individual card in the main section, then move to the desired subsection, could you just create a button that only selects cards in the main section?
Thanks!