Align rotated div with another div - html

Question

I have a main div (the red div in the fiddle) that has a smaller vertical tab on the side (the blue div in the fiddle).
The RED div is standard BUT the Blue div is rotated through 90 degrees (as I need to have vertical text in it). This is where the problems starts.
The red div is vertically positioned at 50% so it is in the middle of the page and locked with scrolling etc.
I want to align the blue div so that the top edge of the blue div is at the same Y position as the top edge of the red div.
I would prefer NOT to use jQuery but can do if required.
Desired output :
Fiddle is here : http://jsfiddle.net/kBKf6/
Here is the code I am using :
<div id="main" style="position: fixed; top: 50%; margin-top: -250px; left:0; height: 500px; width: 450px; background-color:red;">
Main Content Div
</div>
<div id="vertical_div" style="overflow:hidden; position: fixed; left:350px; height:40px; width:200px; margin: auto; background-color:blue; text-align:center; color:white; -webkit-transform: rotate(90deg) translate(-50%, -50%); -moz-transform: rotate(90deg) translate(-50%, -50%); -ms-transform: rotate(90deg) translate(-50%, -50%); -o-transform: rotate(90deg) translate(-50%, -50%); transform: rotate(90deg) translate(-50%, -50%);">
Side Tab
</div>

Answer 1

You don't need JS to align the rotated div. You can define a transform origin in CSS then, it becomes easy to align.
Side note : You can remove the -moz- and -o- vendor prefixes see caniuse
DEMO
HTML :
<div id="main">Main Content Div
<div id="verticaldiv">Side Tab</div>
</div>
CSS :
#main {
position: fixed;
top: 50%;
margin-top: -250px;
left:0;
height: 500px;
width: 450px;
background-color:red;
}
#verticaldiv {
overflow:hidden;
position: absolute;
left:100%;
bottom:100%;
height:40px;
width:200px;
background-color:blue;
text-align:center;
color:white;
-webkit-transform: rotate(90deg);
-ms-transform: rotate(90deg);
transform: rotate(90deg);
-ms-transform-origin:0 100%;
-webkit-transform-origin: 0 100%;
transform-origin: 0 100%;
}

Answer 2

You can also do it without relying on hardcoded sizes that move your div into position, but you need a wrapper around your .verticaldiv
demo:
http://jsfiddle.net/MCr6f/
demo 2:
http://jsfiddle.net/9LtKw/ (to show that different sizes don't matter)
html:
<div class="one">
Hello
<div class="pivot">
<div class="two">
Pretty!
</div>
</div>
</div>
css:
.one {
background: red;
position: relative;
float: left;
/*strange and difficult sizes*/
font-size: 3.237827em;
padding: 10px;
}
.pivot {
position: absolute;
top: 0;
right: 0;
-webkit-transform: rotate(90deg);
-moz-transform: rotate(90deg);
transform: rotate(90deg);
width: 0px;
height: 0px;
}
.two {
background: blue;
color: white;
position: absolute;
left: 0;
bottom: 0;
/*strange and difficult sizes*/
font-size: 12px;
padding: 0.3em;
}