Hi Mat, for backing up your v3.2 custom UI you'd want to make a copy of any files you have changed or added to MoI's default installation. It's probably easiest to make a copy of the entire application folder. The only thing separate from that is your moi.ini file, you can find where that is located at by going to MoI's Options dialog and clicking the "Edit .ini file" button inside the General section, a dialog will pop up showing you the path to the moi.ini file.

For V4 it's not generally possible to just directly copy over your V3 UI in place of the V4 UI because that would then miss any new things added in the V4 UI, and the UI structure of V4 is slightly different than V3. The main differences are that V4 uses the standard CSS flexbox for arranging things while V3 used the early Webkit specific and now deprecated flexbox which is similar but has slightly different property names. So there are a few changes with different property names used in moi.css although about 99% of moi.css is the same.

But you generally need to merge your modifications into V4 in the same way you applied them in V3, not just copy your entire V3 file right over in place of the V4 one.

- Michael