Wow... I really wish I read this last week, could have come in handy... I was surprised the field size was so small all things considered... and no warning if your markup code is too long either- it just cuts off.
you do not need to increase that lenght... create a class in your CSS that will contain the style you need, and use that class name inside your htmlmarkup... this will be compliant.
Open the DB, click on the table in which you wish to change the value (usergroup), click structure, then click the little pen(change) to edit the field you wish to change (title). Change the field lenth/value and save.
This is fine if you are not entering huge amounts of code, but as vbenhancer says, and particularly if you are doing something large or something you want to use in multiple groups etc a CSS class would be the way to do it.