I’m afraid that is not supported in the current web client and it isn’t currently a feature of the web 2 client, but I’ll add it to the list of possible future features.
The web 2 client does have more room to display the marker description and also uses tooltips to display the whole text if it won’t fit.
I’m afraid customising the current web client is very difficult – you’d pretty much have to start from scratch. The new web 2 client uses much more straightforward HTML5/JQuery/Bootstrap technology and the public CatDV REST API so will be much easier for any competent web developer to customise.
But maybe we’ll be able add this as a standard feature and you won’t need to…