Selectors ( selector { property : value } )

Type selectors

tagName : one of the existing HTML tags : all the tags of that sort will be affected

E.g. : a, li, ul
strong {color: red }

Class Selector

Solitary class selectors
.className : style that will be applied to any area defined by a surrounding tag or DIV or SPAN

E.g. : .question {font-weight: bold}
<h3 class="question">What are solitary class selectors ?</h3>

<div class="question"><h2>important question</h2><h2>less important question</h2><div>
<p>And now let's ask the question : <span class="question">Is it an important question ?<span></p>

selects only a specific type of element of that class

E.g. : h3.question {font-weight: bold}

ID Selector

in any valid HTML document there should only be one heading 1 with an ID of title.

E.g. : #TheQuestion
<h3 id="TheQuestion">What is the difference between id and class ?</H3>

To learn more about selectors :