Mobilde Header bozuluyor

/* header */
header {
    background-color: rgb(0, 0, 0) !important;
	width: 100%;
}
header .center {
    background: url(../images/header-alt-bg.png) no-repeat top center;
    height: 253px;
    z-index: 10;
}

<header>
<div class="center">
<nav class="nav-menu">
<ul>
<li class="home"><a href="index.html" title=""></a></li>					
<li><a href="#" title="">Üye Girişi</a>|</li>						
<li><a href="#" title="">Üye Ol</a></li>
</ul>
</nav>
<div class="header-sepet">
<span class="tel">444 4 444</span>
</div>
<h1 class="logo">
<a href="#">Damasko Tekstil</a>
</h1>
<nav class="menu">
<ul>
<li><a title="" href="#" >ANA SAYFA</a></li>
</ul>
</nav>
<div class="search">
<form id="mainSearchForm" name="mainSearchForm" method="get" action="#">

<input type="text" id="q" name="q" placeholder=" Sitede arama..." value="" />

<button type="submit">Ara</button>			
</form>
</div>
</div>
</header>