Change CSS when user is logged in

Here is another CSS-only approach, without any inline-PHP and needless CSS-spam in the head.
If your theme is correctly using body_class() and a user is logged in, WordPress adds a class “logged-in” to the body-element, so we can use this in our stylesheet:

<--logged out-->
.sellertitle {
  float: none;
  width: 49%;      
}

.otherseller {
  display: none;
}

<--logged in-->
.logged-in .sellertitle {
  float: left;     
}

.logged-in .otherseller {
  display: inline;
}