Div does not want to align to center..

Hi Guys,

After 4 hours of not achieving anything, I hope you can help me…

This is the code in a theme template (header). It is a responsive menu that is aligned on the left (nav id=”main-nav” class=”primary menu center”.

I want it aligned to the center.

<header id="header" class="container span-12 ">

						<h1 id="logo" class="center">
				<a href="https://maasbergbv.nl/website/" title="Maasberg BV" rel="home">Maasberg BV</a>
			</h1>

			<div id="menu3"><div id="menu2"><nav id="main-nav" class="primary menu center">
				<ul id="menu-responsive-select-menu" class="menu"><li id="menu-item-6682" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-6682"><a href="https://www.madza-wordpress-premium-themes.com/wp-donatenow/">Home</a></li>
<li id="menu-item-6705" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children menu-item-6705"><a href="https://maasbergbv.nl/website/?page_id=6029" class="w-sub">Blog</a>
<ul class="sub-menu" style="display: none;">
	<li id="menu-item-7066" class="menu-item menu-item-type-taxonomy menu-item-object-category menu-item-7066"><a href="https://maasbergbv.nl/website/?cat=1">Geen categorie</a></li>
</ul>
</li>
<li id="menu-item-6708" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-6708"><a href="https://maasbergbv.nl/website/?page_id=4900">Portfolio</a></li>
<li id="menu-item-6707" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-6707"><a href="https://maasbergbv.nl/website/?page_id=4975">Contacts</a></li>
</ul><select class="select-menu"><option value="#">Navigate to...</option><option value="https://www.madza-wordpress-premium-themes.com/wp-donatenow/">&nbsp;Home</option><option value="https://maasbergbv.nl/website/?page_id=6029">&nbsp;Blog</option><option value="https://maasbergbv.nl/website/?cat=1">–&nbsp;Geen categorie</option><option value="https://maasbergbv.nl/website/?page_id=4900">&nbsp;Portfolio</option><option value="https://maasbergbv.nl/website/?page_id=4975">&nbsp;Contacts</option><option value="#">Navigate to...</option><option value="https://www.madza-wordpress-premium-themes.com/wp-donatenow/">&nbsp;Home</option><option value="https://maasbergbv.nl/website/?page_id=6029">&nbsp;Blog</option><option value="https://maasbergbv.nl/website/?page_id=4900">&nbsp;Portfolio</option><option value="https://maasbergbv.nl/website/?page_id=4975">&nbsp;Contacts</option></select>			</nav></div></div>

		</header>

The CSS is here:

.menu li {
  display: inline;
  float: center;
}
#menu3 {width:100%;}
#menu2 {float: center;
position: relative;
width: 100%;
margin-right: 50%;
background-color: #fff;
max-width: 700px;}
.menu.tertiary li,
.menu.secondary li {
  margin-right: 8px;
  padding-right: 8px;
}
.menu.tertiary li:last-child,
.menu.secondary li:last-child {
  margin-right: 0;
  padding-right: 0;
  border-right: none;
}
.menu.tertiary li .sub-menu,
.menu.secondary li .sub-menu {
  display: none;
}
.menu.tertiary li {
  border-right: 1px solid rgba(255, 255, 255, 0.2);
}
.menu.secondary li {
  border-right: 1px solid rgba(0, 0, 0, 0.2);
}
.select-menu {
  display: none;
}
#main-nav {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  -ms-box-sizing: border-box;
  box-sizing: border-box;
}
#main-nav ul {
  line-height: 1;
  float: center;
  display: block;
}
#main-nav ul li {
  float: left;
  color: #ffffff;
  background-color:#ba0808;
}
#main-nav ul li {
  position: relative;
  display: block;
  font-size: 12px;
  font-weight: bold;
  text-transform: uppercase;
}
#main-nav ul li a {
  display: block;
  outline: none;
  cursor: default;
}
#main-nav ul li a[href] {
  cursor: pointer;
  margin-top:15px;
}
#main-nav ul li.menu-item-hover > a,
#main-nav ul li.current-menu-item > a {
  color: #ffffff;
  background-color:#ba0808;
}
#main-nav ul.sub-menu {
  display: none;
  position: absolute;
  width: 180px;
  left: 10px;
  margin-top: 0px;
  border-top: 2px solid #ffa01f;
  -webkit-box-shadow: 0 4px 10px 0 rgba(0, 0, 0, 0.2);
  -moz-box-shadow: 0 4px 10px 0 rgba(0, 0, 0, 0.2);
  box-shadow: 0 4px 10px 0 rgba(0, 0, 0, 0.2);
  z-index: 300;
  background-color: #fff;
}
#main-nav ul.sub-menu li {
  position: relative;
  width: 100%;
  font-size: 12px;
  line-height: 14px;
  padding: 0;
  border-top: 1px solid #eaeaea;
  font-weight: normal;
  text-transform: none;
}
#main-nav ul.sub-menu li a {
  background-color: transparent;
  padding: 10px 10px;
}
#main-nav ul.sub-menu li a:hover {
  background-color: rgba(0, 0, 0, 0.02);
}
#main-nav ul.sub-menu li a.w-sub:after {
  font-family: 'fontello';
  font-style: normal;
  font-weight: normal;
  speak: none;
  display: inline-block;
  text-decoration: inherit;
  width: 1em;
  content: '\61';
  position: absolute;
  right: 0;
}
#main-nav ul.sub-menu li:first-of-type {
  position: relative;
  border-top: none;
}
#main-nav ul.sub-menu li.menu-item-hover > a,
#main-nav ul.sub-menu li.current-menu-item > a {
  color: #ffa01f;
  padding: 10px 10px;
  border-top: none;
}
#main-nav ul.sub-menu li .sub-menu {
  top: -2px;
  left: 180px;
}
#main-nav ul.sub-menu li .sub-menu li:first-of-type:before {
  display: none;
}
/*