For mobile users: Make the Create post button float

edit: Make button float in feeds, too.
edit2: Fix inconsistency

#side_pane div:nth-child(1) div div div:nth-child(2) a.btn-primary,  
#side_pane div:nth-child(1) div div div:nth-child(1) a.btn-primary {  
  position: fixed;  
  top: 17vh;  
  left: 77vw;  
  max-width: 60pt;  
  overflow: hidden;  
  z-index: 999;  
  box-shadow: 5pt 5pt 30pt black;  
}