Aligning DIVs vertically - css

Question

How do I align the red box with the gray box vertically?
http://jsfiddle.net/sLZzK/1/
I need several box combinations like that on my page, which is why I cannot simply push the red box up manually. A negative margin won't work either, since I do not know in advance how much content will be in the gray box. And the red box must overlap other page content, hence the absolute positioning. (http://jsfiddle.net/xMm82/)
CSS:
body {
padding: 0;
margin: 10px;
}
.left_div {
margin-bottom: 10px;
width: 300px;
height: 70px;
border: 1px solid gray;
}
.right_div {
position: absolute;
border: 1px solid red;
left: 311px;
width: 200px;
height: 200px;
}
HTML:
<div class="left_div">gray box
<div class="right_div">red box</div>
</div>

Answer 1

Why are you using absolute positioning for such structure? In the case the better solution is to use float: left for each div. If you want to have two divs aligned vertically use display: table-cell rule. Here it is:
FIDDLE
UPDATE: Try to use this:
FIDDLE

Answer 2

what I've understood is you want gray box on top of Red box:
first of all wrap them in a parent div.
set the width of wrapper to desirable width.
set width to 100%(both red and gray) and you are done !! (fiddle)
If you want to arrange them horizontally:
left_div will be wrapper
it will contain 2 child div's
left one will have content and right one will be red box.(fiddle)

Answer 3

I would do it this way:
HTML:
<div class="container">
<div class="left_div">gray box</div>
<div class="right_div yellow">red box</div>
<div class="clr"></div>
</div>
CSS:
.container:not(:last-child){margin-bottom: 10px;}
.left_div,.right_div{float:left;}
.clr{clear:both;}
Fiddle here.

Answer 4

use float to arrange vertically and clear:both to prevent any errors
here's the corrected one
.left{
float:left;
width: 300px;
}
.right{
float:left;
width: 200px;
}
.left_div {
width: 300px;
height: 70px;
border: 1px solid gray;
}
.right_div {
border: 1px solid red;
width: 200px;
height: 200px;
}
<div class="left">
<div class="left_div">
</div>
</div>
<div class="right">
<div class="right_div">
</div>
</div>
<div style="clear:both"></div>
http://jsfiddle.net/sLZzK/8/

Answer 5

There you go: http://jsfiddle.net/sLZzK/14/
HTML:
<div class="wrapper">
<div class="left_div">gray box</div>
<div class="right_div">red box</div>
</div>
CSS:
.wrapper {
border: 1px solid #369;
padding: 10px;
}
.wrapper > div {
display: inline-block;
vertical-align: middle;
}
You might also want to read about flexbox which will give you a similar and more consistent result, however it's not fully supported on various browsers yet.