The best way to find what classes to use is to use the inspector in the browser togheter with the inspect element.
(for chrome this is ctrl+shift +i followed by ctrl+shift+c)
this will allow you find the elemnts easier by hovering/clicking.
it still might require you to dig a little further through the elements in the inspector (right side of the screen)
in perspective you can add classes, this will get a suffic "psc-" so will be "psc-CLASSNAME"
you can use this to narrow down to a specifc elemnts by adding the css slsector for this class infront with a dot followed by the class ".psc-CLASSNAME .ia_labelComponent" (sometimes with or sometimes without space depending on what you want to select)
you could also use domId, but probably not as usefull in perspective.
you can look up mayn of my posts for other tips and tricks, i have answered many css related questions