How to change css styling for different lines within a paragraph in javascript

So I have this code that defined a variable called circle, and appended it a title. The title has four lines, first is the country, second is the price, 3rd is the value, and 4th is the gdppc. Now I want to make the gdppc a larger font size than the previous 3 variables. This would require me to style gdppc separately from the others (currently they are all styled by this css called tipsy). However, I don't know how exactly would I do that.

circles.append("title")
        .text(function(d) { return d.country + "<br/> " + "Price=" + d.trust 
        + ", Value=" + d.business + "<br/> " + d.gdppc; }); 

$(".circles").tipsy({ gravity:'nw', html: true,});

The idea is probably to make gdppc a separate variable, and style it separately.