爲什麼孩子的父母的兄弟姐妹與他們的父母有不同的表現？

我有一個HTML結構是這樣的：爲什麼孩子的父母的兄弟姐妹與他們的父母有不同的表現？

0.body 
     ->>1.background 
      ->>2.leftwing 
      ->>2.rightwing 
      ->>2.content block 
      ->>3.top-content block 
       ->>4.contacts block 
      ->>4.title block 
       ->>4.edited block

左翼，右翼和內容塊是兄弟。聯繫人，標題和編輯是兄弟姐妹。

這是我的HTML：

<head> 
    <link rel="stylesheet" href="style.css"> 
</head> 
<body> 
    <div class="bckdrp all"> 
     <div class="lftfd all"> 
     </div> 
     <div class="rtfd all"> 
     </div> 
     <div class="bigbox all"> 
      <div class="topbox all"> 
       <div class="lftcnt inlblk all"> 
        contact 
       </div> 
       <div class="midcnt inlblk all"> 
        title 
       </div> 
       <div class="rtcnt inlblk all"> 
        edited 
       </div> 
      </div> 
      <div class="topnav all"> 
       <div class="toppnt all"> 
        up 
       </div> 
      </div> 
      <div class="midbox all"> 
       <div class="lftspc inlblk all"> 
       </div> 
       <div class="midspc inlblk all"> 
        <div class="super all"> 
         LONG 
         <!--ENLONGATED--> 
        </div> 
       </div> 
       <div class="rtspc inlblk all"> 
        <div class="navpad all"> 
         <!--1--><div class="navcir all">1</div> 
         <!--2--><div class="navcir all">2</div> 
         <!--3--><div class="navcir all">3</div> 
         <!--4--><div class="navcir all">4</div> 
         <!--5--><div class="navcir all">5</div> 
         <!--6--><div class="navcir all">6</div> 
        </div> 
       </div> 
      </div> 
      <div class="botnav all"> 
       <div class="botpnt all"> 
        down 
       </div> 
      </div> 
      <div class="botbox all"> 
       <div class="foot all"> 
        <div class="acc all"> 
         login 
        </div> 
       </div> 
      </div> 
     </div> 
    </div> 
</body>

這是我的CSS：

.bckdrp 
{ 
    background: url("img/bckdrp.jpg") center center no-repeat; 
    background-size: cover; 
    height: 100%; 
    width: 100%; 
} 

.lftfd 
{ 
    background: linear-gradient(to right, rgba(255, 255, 255, 0.8), rgba(255, 255, 255, 0.4), rgba(0, 0, 0, 0.0)); 
    background: -webkit-linear-gradient(left, rgba(255, 255, 255, 0.8), rgba(255, 255, 255, 0.4), rgba(0, 0, 0, 0.0)); 
    background: -o-linear-gradient(left, rgba(255, 255, 255, 0.8), rgba(255, 255, 255, 0.4), rgba(0, 0, 0, 0.0)); 
    background: -moz-linear-gradient(left, rgba(255, 255, 255, 0.8), rgba(255, 255, 255, 0.4), rgba(0, 0, 0, 0.0)); 
    float: left; 
    height: 100%; 
    width: 30%; 
} 

.rtfd 
{ 
    background: linear-gradient(to right, rgba(0, 0, 0, 0.0), rgba(255, 255, 255, 0.4), rgba(255, 255, 255, 0.8)); 
    background: -webkit-linear-gradient(left, rgba(0, 0, 0, 0.0), rgba(255, 255, 255, 0.4), rgba(255, 255, 255, 0.8)); 
    background: -o-linear-gradient(left, rgba(0, 0, 0, 0.0), rgba(255, 255, 255, 0.4), rgba(255, 255, 255, 0.8)); 
    background: -moz-linear-gradient(left, rgba(0, 0, 0, 0.0), rgba(255, 255, 255, 0.4), rgba(255, 255, 255, 0.8)); 
    float: right; 
    height: 100%; 
    width: 30%; 
} 




.inlblk 
{ 
    display: inline-block; 
} 


.bigbox 
{ 
    background-color: blue; 
} 

.topbox 
{ 
    background-color: yellow; 
} 

.all 
{ 
    border: 1px solid rgba(255, 0, 0, 0.5); 
}

這是結果：