Hi @sadjow,
There’s a discussion here on the reasons why… Bootstrap 4 final in next Phoenix release? (Update: No... Phoenix 1.4 uses Milligram)
If you ever need any help on things like this, feel free to ask. I’m using bootstrap 4 in a LV project and it was quite straightforward to get going with a couple of small pointers in how the assets setup works. You’ve obviously figured it out now!