一模一样的代码，为什么我的LOGO看不到？

@charset "utf-8";

/* CSS Document */

.public-header{

height:120px;

}

.public-header .header-logo{

float:left;

margin-top:40px;

}

.public-header .header-logo .a{

width:182px;

height:54px;

background:url("../images/index-header-logo.png");

}

.public-header .header-nav{

float:right;

font-size:14px;

}

.public-header .header-nav .item{

float:left;

margin-top:44px;

margin-left:50px;

}

.public-header .header-nav .a{

    color:#333;

}

.public-container{

position:relative;

margin:0 auto;

width:1100px;

}

.public-footer{

height:320px;

background:#F00;

}