懸停時按鈕會閃爍閃爍的黑色邊框？

當我將鼠標懸停在其中一個按鈕上時，它會閃爍黑色邊框，然後消失。代碼中沒有邊框。如果導致任何問題，我也使用Chrome。我不想在這裏邊界。懸停時按鈕會閃爍閃爍的黑色邊框？

下面是代碼：

body { 
 
    background: #5544aa; 
 
    } 
 

 
nav { 
 
    background: rgba(0, 0, 0, .2); 
 

 
\t border-radius: 0px; 
 
\t box-shadow: 2px 2px 3px rgba(255,255,255,0.1), -2px -2px .5px rgba(0,0,0,0.3); 
 
\t } 
 
\t 
 
nav ul { 
 
    width: 950px; 
 
    margin: 0 auto; 
 
} 
 

 
nav ul li { 
 
    list-style-type: none; 
 
    width: 150px; 
 
\t margin-top: 15px; 
 
    float: left; 
 
    border: none; 
 
    text-align: center; 
 
} 
 

 
li a { 
 
    text-decoration: none; 
 
    color: #555555; 
 
\t border-radius: 0px; 
 
\t box-shadow: 0 0 0 #000; 
 
\t text-shadow: 0 1px 1px rgba(0, 0, 0, .5); 
 
    line-height: 50px; 
 
    display: block; 
 
\t transition: all ease-in-out 250ms; 
 
} 
 
li a:hover { 
 
    background: rgba(255, 255, 255, .1); 
 
\t box-shadow: 0 8px 8px -6px #333, inset 0 0 3px rgba(0,0,0,0.1); 
 
\t color: #222222; 
 
\t padding: 0px 0px; 
 
\t text-shadow: 0 2px 4px rgba(0, 0, 0, .5); 
 
         }

<nav> 
 
    <ul> 
 
     <li> <a href="index.html">Home</a> 
 

 
     </li> 
 
     <li> <a href="services.html">Products</a> 
 

 
     </li> 
 
     <li> <a href="contacts.html">Contacts</a> 
 

 
     </li> 
 
     <li> \t <a href="about.html">About</a> 
 

 
     </li> 
 
    </ul> 
 
</nav>

來源

2015-10-24 Akados