Recompiling custom.css

[Meddysong]

I was amending a database template last night when I noticed an unexpected result on refreshing. All of the values for the name field below have custom formatting. But where the name Ian appears, the background colour for the ipsBadge no longer appeared:

A check confirmed that the correct class (.ipsBadge_style12) was included in the HTML:

And I confirmed that it was still included and was correctly written in the ACP's custom.css:

But when I look at the custom.css file which is being downloaded, it's missing:

I've tried editing its colour value and even creating a new style, but saving the changes isn't causing my custom.css file to be rebuilt.

What do I need to do to recompile my custom.css? And what could be causing this behaviour?