1. Find the element you wish to target
2. Right click that item
3. Select Inspect from the contextual menu.
4. When this brings up the developer's toolbox, look for the CSS hook chain (circled in red)

All modern browsers have similar functionality, but the placement of the listing varies. The screenshot is Google Chrome.

In this example, the header "The Road to Enlightenment" is an h3 embedded in the div#zen-preamble.