add translucent balck background for history rendering

Change-Id: I9da69bdb29bb780776355e79fab61d5d9bb844a4
Reviewed-on: https://gerrit.libreoffice.org/11583
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>