You can't currently get a multi-line parameter title, which is what is sounds like you're looking for. If you put this in the Idea section I'll vote for it. Also you can't currently format the text of a parameter or quick filter; this one I think already has an idea out there somewhere.
I've just started using parameters and have developed a little workaround which allows you to format the output (e.g. % figure) of a parameter.
- create the parameter and turn on "parameter control"
- create a calculated field where the calculation = parameter (so the result is simply that of the parameter)
- create a new sheet with the new calculated field on the Text panel
- format the output of the calculated field, adjust number format, font, size, colour, etc.
- on your dashboard show the parameter control, untick the "show readout" option", but leave the slider and buttons selected.
- float the parameter control and the worksheet containing the parameter output (e.g. % figure) and align them in whichever way you want.
Limitation: this workaround doesn't enable you to format the "Type in" field of a parameter.