XF 1.4 Increase default font size Message Body -Help with Style Property

Hi ,
I want to increase the default font size for post content,(message content),
I tried by editing style properties,
there are so much to choose with,
I think, i am doing something wrong, so changes are not reflected,

i am trying in these sections

Message List
Message Container
User Info Container
User Info Block
Avatar Holder
User Text Block
Extra User Info
Content Container
Main Content
Controls Area

Also i want to change the background color of, category ribbon
there are so much css styling :( i cant find the right one,
only i need to change these two things,
someone tell the correct property please.