如何居中导航栏？

我正在为我的网站制作一个导航栏。我希望它居中。这是我的样式和HTML文件。

@import url(http://fonts.googleapis.com/css?family=Open+Sans:400,700);
#cssmenu,
#cssmenu ul,
#cssmenu ul li,
#cssmenu ul li a,
#cssmenu #menu-button {
  margin: 0;
  padding: 0;
  border: 0;
  list-style: none;
  line-height: 1;
  display: block;
  position: relative;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}
#cssmenu:after,
#cssmenu > ul:after {
  content: ".";
  display: block;
  clear: both;
  visibility: hidden;
  line-height: 0;
  height: 0;
}
#cssmenu #menu-button {
  display: none;
}

#nav ul {
    display: inline-block;
    list-style-type: none;
}
#cssmenu {
  width: auto;
  font-family: 'Comic Sans Ms', Helvetica, sans-serif;
  background: #39b1cc;
  background: -moz-linear-gradient(top, #51bbd2 0%, #2d97af 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #51bbd2), color-stop(100%, #2d97af));
  background: -webkit-linear-gradient(top, #51bbd2 0%, #2d97af 100%);
  background: -o-linear-gradient(top, #51bbd2 0%, #2d97af 100%);
  background: -ms-linear-gradient(top, #51bbd2 0%, #2d97af 100%);
  background: linear-gradient(to bottom, #51bbd2 0%, #2d97af 100%);
}
#cssmenu > ul {
  background: url('images/bg.png');
  box-shadow: inset 0 -3px 0 rgba(0, 0, 0, 0.05);
}
#cssmenu.align-right > ul > li {
  float: right;
}
#cssmenu > ul > li {
  float: left;
  display: inline-block;
}
#cssmenu.align-center > ul {
  float: none;
  text-align: center;
}
#cssmenu.align-center > ul > li {
  float: none;
}
#cssmenu.align-center ul ul {
  text-align: left;
}
#cssmenu > ul > li > a {
  padding: 18px 25px 21px 25px;
  border-right: 1px solid rgba(80, 80, 80, 0.12);
  text-decoration: none;
  font-size: 15px;
  font-weight: 700;
  color: #d3eced;
  text-transform: uppercase;
  letter-spacing: 1px;
}
#cssmenu > ul > li:hover > a,
#cssmenu > ul > li > a:hover,
#cssmenu > ul > li.active > a {
  color: #ffffff;
  background: #32a9c3;
  background: rgba(0, 0, 0, 0.1);
}
#cssmenu > ul > li.has-sub > a {
  padding-right: 45px;
}
#cssmenu > ul > li.has-sub > a::after {
  content: "";
  position: absolute;
  width: 0;
  height: 0;
  border: 6px solid transparent;
  border-top-color: #d3eced;
  right: 17px;
  top: 22px;
}
#cssmenu > ul > li.has-sub.active > a::after,
#cssmenu > ul > li.has-sub:hover > a {
  border-top-color: #ffffff;
}
#cssmenu ul ul {
  position: absolute;
  left: -9999px;
  top: 60px;
  padding-top: 6px;
  font-size: 13px;
  opacity: 0;
  -webkit-transition: top 0.2s ease, opacity 0.2s ease-in;
  -moz-transition: top 0.2s ease, opacity 0.2s ease-in;
  -ms-transition: top 0.2s ease, opacity 0.2s ease-in;
  -o-transition: top 0.2s ease, opacity 0.2s ease-in;
  transition: top 0.2s ease, opacity 0.2s ease-in;
}
#cssmenu.align-right ul ul {
  text-align: right;
}
#cssmenu > ul > li > ul::after {
  content: "";
  position: absolute;
  width: 0;
  height: 0;
  border: 5px solid transparent;
  border-bottom-color: #ffffff;
  top: -4px;
  left: 20px;
}
#cssmenu.align-right > ul > li > ul::after {
  left: auto;
  right: 20px;
}
#cssmenu ul ul ul::after {
  content: "";
  position: absolute;
  width: 0;
  height: 0;
  border: 5px solid transparent;
  border-right-color: #ffffff;
  top: 11px;
  left: -4px;
}
#cssmenu.align-right ul ul ul::after {
  border-right-color: transparent;
  border-left-color: #ffffff;
  left: auto;
  right: -4px;
}
#cssmenu > ul > li > ul {
  top: 120px;
}
#cssmenu > ul > li:hover > ul {
  top: 52px;
  left: 0;
  opacity: 1;
}
#cssmenu.align-right > ul > li:hover > ul {
  left: auto;
  right: 0;
}
#cssmenu ul ul ul {
  padding-top: 0;
  padding-left: 6px;
}
#cssmenu.align-right ul ul ul {
  padding-right: 6px;
}
#cssmenu ul ul > li:hover > ul {
  left: 180px;
  top: 0;
  opacity: 1;
}
#cssmenu.align-right ul ul > li:hover > ul {
  left: auto;
  right: 100%;
  opacity: 1;
}
#cssmenu ul ul li a {
  text-decoration: none;
  font-weight: 400;
  padding: 11px 25px;
  width: 180px;
  color: #777777;
  background: #ffffff;
  box-shadow: 0 2px 2px rgba(0, 0, 0, 0.1), 1px 1px 1px rgba(0, 0, 0, 0.1), -1px 1px 1px rgba(0, 0, 0, 0.1);
}
#cssmenu ul ul li:hover > a,
#cssmenu ul ul li.active > a {
  color: #333333;
}
#cssmenu ul ul li:first-child > a {
  border-top-left-radius: 3px;
  border-top-right-radius: 3px;
}
#cssmenu ul ul li:last-child > a {
  border-bottom-left-radius: 3px;
  border-bottom-right-radius: 3px;
}
#cssmenu > ul > li > ul::after {
  position: absolute;
  display: block;
}
#cssmenu ul ul li.has-sub > a::after {
  content: "";
  position: absolute;
  width: 0;
  height: 0;
  border: 4px solid transparent;
  border-left-color: #777777;
  right: 17px;
  top: 14px;
}
#cssmenu.align-right ul ul li.has-sub > a::after {
  border-left-color: transparent;
  border-right-color: #777777;
  right: auto;
  left: 17px;
}
#cssmenu ul ul li.has-sub.active > a::after,
#cssmenu ul ul li.has-sub:hover > a::after {
  border-left-color: #333333;
}
#cssmenu.align-right ul ul li.has-sub.active > a::after,
#cssmenu.align-right ul ul li.has-sub:hover > a::after {
  border-right-color: #333333;
  border-left-color: transparent;
}
@media all and (max-width: 800px), only screen and (-webkit-min-device-pixel-ratio: 2) and (max-width: 1024px), only screen and (min--moz-device-pixel-ratio: 2) and (max-width: 1024px), only screen and (-o-min-device-pixel-ratio: 2/1) and (max-width: 1024px), only screen and (min-device-pixel-ratio: 2) and (max-width: 1024px), only screen and (min-resolution: 192dpi) and (max-width: 1024px), only screen and (min-resolution: 2dppx) and (max-width: 1024px) {
  #cssmenu {
    background: #39b1cc;
  }
  #cssmenu > ul {
    display: none;
  }
  #cssmenu > ul.open {
    display: block;
    border-top: 1px solid rgba(0, 0, 0, 0.1);
  }
  #cssmenu.align-right > ul {
    float: none;
  }
  #cssmenu.align-center > ul {
    text-align: left;
  }
  #cssmenu > ul > li,
  #cssmenu.align-right > ul > li {
    float: none;
    display: block;
  }
  #cssmenu > ul > li > a {
    padding: 18px 25px 18px 25px;
    border-right: 0;
  }
  #cssmenu > ul > li:hover > a,
  #cssmenu > ul > li.active > a {
    background: rgba(0, 0, 0, 0.1);
  }
  #cssmenu #menu-button {
    display: block;
    text-decoration: none;
    font-size: 13px;
    font-weight: 700;
    color: #d3eced;
    padding: 18px 25px 18px 25px;
    text-transform: uppercase;
    letter-spacing: 1px;
    background: url('images/bg.png');
    cursor: pointer;
  }
  #cssmenu ul ul,
  #cssmenu ul li:hover > ul,
  #cssmenu > ul > li > ul,
  #cssmenu ul ul ul,
  #cssmenu ul ul li:hover > ul,
  #cssmenu.align-right ul ul,
  #cssmenu.align-right ul li:hover > ul,
  #cssmenu.align-right > ul > li > ul,
  #cssmenu.align-right ul ul ul,
  #cssmenu.align-right ul ul li:hover > ul {
    left: 0;
    right: auto;
    top: auto;
    opacity: 1;
    width: 100%;
    padding: 0;
    position: relative;
    text-align: left;
  }
  #cssmenu ul ul li {
    width: 100%;
  }
  #cssmenu ul ul li a {
    width: 100%;
    box-shadow: none;
    padding-left: 35px;
  }
  #cssmenu ul ul ul li a {
    padding-left: 45px;
  }
  #cssmenu ul ul li:first-child > a,
  #cssmenu ul ul li:last-child > a {
    border-radius: 0;
  }
  #cssmenu #menu-button::after {
    display: block;
    content: '';
    position: absolute;
    height: 3px;
    width: 22px;
    border-top: 2px solid #d3eced;
    border-bottom: 2px solid #d3eced;
    right: 25px;
    top: 18px;
  }
  #cssmenu #menu-button::before {
    display: block;
    content: '';
    position: absolute;
    height: 3px;
    width: 22px;
    border-top: 2px solid #d3eced;
    right: 25px;
    top: 28px;
  }
  #cssmenu > ul > li.has-sub > a::after,
  #cssmenu ul ul li.has-sub > a::after {
    display: none;
  }
}

<html>
<head>
<meta charset='utf-8'>
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <link rel="stylesheet" href="styles.css">
   <script src="http://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
   <script src="script.js"></script>
   <title>Hugo de Heer</title>

</head>
<body>
    <body background="images/background.png">

<div style="text-align: center;">
    <IMG SRC="images/logo.png" ALT="image"></div>

<div id='cssmenu'>
<ul>
   <li><a href='#'><span>Home</span></a></li>
   <li class='has-sub'><a href='#'><span>Algemeen</span></a>
      <ul>
         <li class='#'><a href='#'><span>Over mijzelf</span></a></li>

         <li class='#'><a href='#'><span>Mijn hond</span></a>

         </li>
      </ul>
   </li>
   <li class='has-sub'><a href='#'><span>Hobby's</span></a>
        <ul>
      <li class='has-sub'><a href='#'><span>Gamen</span></a>
      <ul>
         <li class='#'><a href='#'><span>Playstation 4</span></a></li>

         <li class='#'><a href='#'><span>Pc Games</span></a></li>
         </li>   
      </ul> 
   </li>
      <li class='has-sub'><a href='#'><span>Sport</span></a> 
      <ul>
         <li class='#'><a href='#'><span>Voetbal</span></a></li>

         <li class='#'><a href='#'><span>Tafeltennis</span></a></li>
         </li>   
      </ul> </ul>
   </li>      
    <li class='has-sub'><a href='#'><span>Vakantie</span></a>   
      <ul>
         <li class='#'><a href='#'><span>Veluwe</span></a></li>

         <li class='#'><a href='#'><span>België en Duitsland</span></a>
         </li>
      </ul>
   </li>
   <li class='has-sub'><a href='#'><span>Muziek</span></a>  
      <ul>
         <li class='#'><a href='#'><span>Orgel</span></a></li>

         <li class='#'><a href='#'><span>Trommelen vroeger</span></a>
         </li>
      </ul>
   </li>

</div>





</body>

</html>