DIV position issues - css

Question

I'm trying to position my DIVs as below
Logo / Menu / Social
Intro-left / intro-right
backpicture
Middle-1
bottom-left / bottom right
The issue is that for the moment DIVs are displayed like this (see JSFiddle http://jsfiddle.net/A4Sn8/1/ ):
Logo / Menu
Social
backpicture
Intro-left / intro-right
Middle-1
bottom-left
bottom right
In summary, my "social" DIV is below the menu instead of on its right. Bottom-right DIV is under bottom-left instead of on its right and backpicture is before Intro-left and intro-right instead of after.
How could I fix this?
Many thanks
HTML
<div id="logo">Logo</div> <!-- End DIV Logo -->
<div id="mainmenu">
<ul>
<li>
<h5>Menu I</h5>
<ul>
<li><a title="" href="">Biography</a> </li>
<li><a title="" href="">Publications</a> </li>
</ul>
<li>
<h5>Menu 2</h5>
<ul>
<li><a title="" href="">Demo</a> </li>
<li><a title="" href="">Features</a> </li>
<li><a title="" href="">Comparison</a> </li>
</ul>
</li>
<li>
<h5>Menu 3</h5>
<ul>
<li><a title="" href="">Item 1</a> </li>
<li><a title="" href="">Item 2</a> </li>
<li><a title="" href="">Item 3</a> </li>
</ul>
</li>
<li>
<h5>Menu 4</h5>
<ul>
<li><a title="" href="">ddfd</a> </li>
<li><a title="" href="">dsfd</a> </li>
</ul>
</li>
</ul>
</div> <!-- End DIV Main Menu -->
<div id="social">Social</div>
<div id="intro-left"></div>
<div id="intro-right">
<div id="content-headline"><h1>Novitates autem si spem</h1></div> <!-- End DIV Content headline-->
<p>Novitates sit.</p>
</div>
<div id="backpicture">backpicture</div>
<div id="middle-1">Middle-1</div>
<div id="bottom-left">bottom-left</div>
<div id="bottom-right">bottom-right</div>
CSS:
#charset"UTF-8";
/* CSS Document */
Html, body {
margin: 0;
padding: 0;
height: 100%;
background: #fff;
font-family: 'Open Sans', sans-serif;
}
#logo {
position: absolute;
top: 35px;
left: 20px;
color: #000;
font-size: 20px;
}
/* mainmenu */
#mainmenu {
margin-top: 35px;
width: 100%;
padding-bottom: 10px;
overflow: hidden;
}
#mainmenu ul {
float: right;
margin: 0;
color: #000;
list-style: none;
}
#mainmenu ul li {
display: inline-block;
float: left;
width: 140px;
line-height: 20px;
}
#mainmenu>ul>li {
margin-left: 20px;
}
#mainmenu ul li a {
display: block;
text-decoration: none;
font-weight:600;
font-size: 12px;
}
#mainmenu ul li a, #mainmenu ul ul:hover li a {
color: #333;
-webkit-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-moz-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-ms-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-o-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-webkit-transition-duration: .4s, .4s, .4s, .4s;
-moz-transition-duration: .4s, .4s, .4s, .4s;
-ms-transition-duration: .4s, .4s, .4s, .4s;
-o-transition-duration: .4s, .4s, .4s, .4s;
transition-duration: .4s, .4s, .4s, .4s;
-webkit-transition-property: all, -webkit-transform;
-moz-transition-property: all, -moz-transform;
-ms-transition-property: all, -ms-transform;
-o-transition-property: all, -o-transform;
transition-property: all, transform;
}
#mainmenu ul ul li a:hover, #mainmenu ul ul li.current-menu-item a {
color: #005EBC;
-webkit-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-moz-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-ms-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-o-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-webkit-transition-duration: .4s, .4s, .4s, .4s;
-moz-transition-duration: .4s, .4s, .4s, .4s;
-ms-transition-duration: .4s, .4s, .4s, .4s;
-o-transition-duration: .4s, .4s, .4s, .4s;
transition-duration: .4s, .4s, .4s, .4s;
-webkit-transition-property: all, -webkit-transform;
-moz-transition-property: all, -moz-transform;
-ms-transition-property: all, -ms-transform;
-o-transition-property: all, -o-transform;
transition-property: all, transform;
}
social {
right: 10px;
Color: blue;
}
p {
color: #333;
font-weight:300;
font-size: 13px;
}
h1 {
color: #00539E;
font-size: 30px;
}
#intro-left {
float: left;
width: 35%;
}
#intro-right {
float: right;
padding-right: 50px;
width: 60%;
}
#backpicture {
height:160px;
width: 100%;
background: blue;
}
#middle-1 {
width: 980px;
background: #c81919;
display: block;
margin-left: auto;
margin-right: auto;
}
#bottom-left {
float: left;
width: 35%;
background: #5421c2;
}
#bottom-right {
float: right;
padding-right: 50px;
width: 60%;
background: #2ec4a6;
}

Answer 1

You are mixing CSS rules with absolute pixel sizes and percent. That is not always a good idea.
You might have this problem, because your padding-right of 50px is larger than the remaining 5% of free space.
I'm not sure what you are trying to achieve, but I guess the bottom elements should be on the same height. Try this:
#bottom-right {
float: right;
padding-right: 5%; /* you defined 50px instead! */
width: 60%;
background: #2ec4a6;
}
Sample: http://jsfiddle.net/A4Sn8/2/

Answer 2

For mainmenu and social to be in one line:
#social {
float:right;
margin-top: 35px;
right: 10px;
color: blue;
}
#mainmenu {
float:left;
margin-top: 35px;
width: 80%;
padding-bottom: 10px;
overflow: hidden;
}
The main issue was width:100% given to #mainmenu. This didnt allowed social block to come to its right. Moreover specifying float:left in #mainmenu and float:right in social did the trick.
One more thing, your social in css didnt had #.