appointment text gets unwanted insertions in agenda view.
In all other views appointment text looks like this: <div><span style="background-color:#F0D408"> 4 - Cityrad 28" </span> (Essen -> Essen) #7817</div>
You could a lot of custom styles in the initialization.
For this purpose, it will be better to use the renderAppointment callback.
The Agenda View is a specific case.
Please, take a look at this example below, that I prepared for you: https://jsfiddle.net/8fv5ny0h/