CSS selector class and element order

问题:

In a HTML table with class of 'testtable', is there any difference between selecting a element in that table with the following two css selectors?

.testtable td{} 

and

td.testtable{} 

回答1:

.testtable td{} selects a td that has a parent with the class testtable, for example:

<table class="testtable">     <td>I'm selected</td> </table> 

td.testtable{} selects a td that has the class testtable, for example:

<table>     <td class="testtable">I'm selected</td> </table> 

文章来源: CSS selector class and element order