css styling sample shows

<style> 
    .classA .classB { *}; // denotes a style class set (A) classB tag labels under classA. 
    .classA, .classB {*}; // represents classA and the classB simultaneously set label stock (B). 
    *} {.classA.classB; // represented as a class set; "class = 'classA classB' " style (C). 
</ style>

// A
<div class="classA">
    <div class="classB">this</div>
</div>
<div class="classC">
　　<div class="classD"></div>
</div>

// B
<div class="classA">this</div>
<div class="classB">this</div>
<div class="classC"></div>
<div class="classD"></div>

// C
<div class="classA classB">this</div>
<div class="classC classD"></div>