CSS Grouping and Nesting Selector

Grouping selectors
In style sheets there are often elements with the same style. To minimize the code, you can group selectors. Separate each selector with a comma.

h1,h2,p
{
color:green;
}

Nesting Selectors

It is possible to apply a style for a selector within a selector.


In the example below, one style is specified for all p elements, one style is specified for all elements with class="marked", and a third style is specified only for p elements within elements with class="marked":

p
{
color:blue;
text-align:center;
}
.marked
{
background-color:red;
}
.marked p
{
color:white;
}

See the original article from here