[css] Create line after text with css

Im trying to make a line after each of my h2 tags. I can´t figure out how I should tell the width, cause the lenght of the h2 headlines is differ from h2 to h2.

I use the :after method to create lines

       h2:after {
       position: absolute;
       content: "";
       height: 2px;
       background-color: #242424;
       width: 50%;
       margin-left: 15px;
       top: 50%;
       } 

Check code here: http://jsfiddle.net/s9gHf/ As you can see the line get too wide, and make the website too wide.

This is the most easy way I found to achieve the result: Just use hr tag before the text, and set the margin top for text. Very short and easy to understand! jsfiddle

h2 {_x000D_
  background-color: #ffffff;_x000D_
  margin-top: -22px;_x000D_
  width: 25%;_x000D_
}_x000D_
_x000D_
hr {_x000D_
  border: 1px solid #e9a216;_x000D_
}

<br>_x000D_
_x000D_
<hr>_x000D_
<h2>ABOUT US</h2>

Here is how I do this: http://jsfiddle.net/Zz7Wq/2/

I use a background instead of after and use my H1 or H2 to cover the background. Not quite your method above but does work well for me.

CSS

.title-box { background: #fff url('images/bar-orange.jpg') repeat-x left; text-align: left; margin-bottom: 20px;}
.title-box h1 { color: #000; background-color: #fff; display: inline; padding: 0 50px 0 50px; }

HTML

<div class="title-box"><h1>Title can go here</h1></div>
<div class="title-box"><h1>Title can go here this one is really really long</h1></div>

Here is another, in my opinion even simpler solution using a flex wrapper:

HTML:

<div class="wrapper">
  <p>Text</p>
  <div class="line"></div>
</div>

CSS:

.wrapper {
  display: flex;
  align-items: center;
}

.line {
  border-top: 1px solid grey;
  flex-grow: 1;
  margin: 0 10px;
}

JSFiddle

I am not experienced at all so feel free to correct things. However, I tried all these answers, but always had a problem in some screen. So I tried the following that worked for me and looks as I want it in almost all screens with the exception of mobile.

<div class="wrapper">
   <div id="Section-Title">
     <div id="h2"> YOUR TITLE
        <div id="line"><hr></div>
     </div>
   </div>
</div>

CSS:

.wrapper{
background:#fff;
max-width:100%;
margin:20px auto;
padding:50px 5%;}

#Section-Title{
margin: 2% auto;
width:98%;
overflow: hidden;}

#h2{
float:left;
width:100%;
position:relative;
z-index:1;
font-family:Arial, Helvetica, sans-serif;
font-size:1.5vw;}

#h2 #line {
display:inline-block;
float:right;
margin:auto;
margin-left:10px;
width:90%;
position:absolute;
top:-5%;}

#Section-Title:after{content:""; display:block; clear:both; }
.wrapper:after{content:""; display:block; clear:both; }

using flexbox:

h2 {
    display: flex;
    align-items: center;

}

h2 span {
    content:"";
    flex: 1 1 auto;
    border-top: 1px solid #000;
}

html:

<h2>Title <span></span></h2>

There's no need for extra wrappers or span elements anymore. Flexbox and Grid can handle this easily.

h2 {_x000D_
  display: flex;_x000D_
  align-items: center;_x000D_
}_x000D_
_x000D_
h2::after {_x000D_
  content: '';_x000D_
  flex: 1;_x000D_
  margin-left: 1rem;_x000D_
  height: 1px;_x000D_
  background-color: #000;_x000D_
}

<h2>Heading</h2>