Its all about the css selectors. CSS boils down to selectors and rules, the part within the {} are the rules and the preceding part is the selector. There are lots of different ways of selecting and learning about the different ways of selecting is the whole key to css mastery.
If you view the source of the rendered page you will see the survey is wrapped in a div with class="panelwrapper survey"
Notice how multiple class names can be specified with white space between them, so in effect this div has both .panelwrapper and .survey applied.
The questions are further contained within a div with class=settingrow
So the css selector:
.survey .settingrow input[type=text]
means select all inputs of type text where the input is nested within a container having class=settingrow which is nested in a container having class=survey
People generally understand simple class selectors easiest
.survey just means select elements with the class survey
But once you learn about more selector possibilities you can pretty much select anything in the markup and apply style rules to it.
Best,
Joe