I’m running the 17.04 Beta 2 version och Ubuntu Mate and it’s great, but I noted that you have removed the Libreoffice-style-breeze and breeze-dark from your version of Libreoffice 5.3. The breeze-dark is very useful for those who want to use a dark gtk theme.
So I found the solution and it was very simple. Just install the libreoffice-style-breeze in the Synaptic package manager. Breeze-dark will install as well. 