It seems that HTML/CSS customization is definitively broken since beta9.
I’m running beta9+82, and it’s very difficult to save modifications in Header, Top, Footer, </ head> and .
Css part is running well.
I must always refresh url to hope having a Save button not greyed.
I believe this had to due with the hellishly complex Ace editor dependency. @eviltrout recently revamped this, are on you a version from today or yesterday? If not, you should update.