Line from left side of screen to end of centered div - css

Question

I want to make a 1 px line from the left side of the screen to the end of a centered div.
The div is centered with margin: auto;.
This image shows how it should look:

Answer 1

Here's an example using calc:
.box{
width:200px;
height:200px;
border:1px solid blue;
margin:0 auto;
}
.line{
border: 1px solid red;
width: calc(((100% - 200px)/2) + 200px);
}
JSFiddle
Browser support

Answer 2

How about this solution? no extra markup needed, cross browser and does not depend on the width of the element
#content {
width:400px;
height: 200px;
margin:auto;
position: relative;
}
#content:before{
content: '';
height: 1px;
background: red;
position: absolute;
top: -5px;
right: 0;
width: 999%; /*a large number*/
}
Demo fiddle

Answer 3

here is another solution and it is cross browser http://jsfiddle.net/9qrSy/3
<div class="inner"></div>
<div class="wrapp"></div>
css
body {
padding:8px;
}
div.wrapp {
width:300px;
height:300px;
border:2px solid green;
margin:auto;
position:relative;
}
div.wrapp:before {
content:'';
position:absolute;
width:100%;
height:1px;
right:0;
top:-6px;
background:blue;
z-index:1;
}
.inner {
width:50%;
float:left;
position:absolute;
height:1px;
left:0;
top:12px;
background:blue;
}

Answer 4

I am not sure if this works in all browsers, but I believe hr takes up all the space you provide it with. Therefore you can give it a large negative left-margin and put it inside the centered div. Instead of a hr-element, you could use an empty div too, which might or might not be easier to use. You can set the border-top style of that div to a wider range of border-types (dotted for example).
<div id="content">
<hr id="bar" />
<div id="realcontent">
Something here
</div>
</div>
With CSS:
#content {
width: 400px;
margin: auto;
color: white;
}
#bar {
margin-left: -1000px;
margin-bottom: 5px;
background: blue;
}
#realcontent {
background-color: #000000;
}