How do I set a background-color for the width of text, not the width of the entire element, using CSS?

Question

Put the text in an inline element, such as a <span>.

<h1><span>The Last Will and Testament of Eric Jones</span></h1>

And then apply the background color on the inline element.

h1 {
    text-align: center; 
}
h1 span { 
    background-color: green; 
}

An inline element is as big as its contents is, so that should do it for you.

Option 1

display: table;

• no parent required

h1 {
    display: table; /* keep the background color wrapped tight */
    margin: 0px auto 0px auto; /* keep the table centered */
    padding:5px;font-size:20px;background-color:green;color:#ffffff;
}

<h1>The Last Will and Testament of Eric Jones</h1>

fiddle

http://jsfiddle.net/J7VBV/293/

more

display: table tells the element to behave as a normal HTML table would.

More about it at w3schools, CSS Tricks and here

---

Option 2

display: inline-flex;

• requires text-align: center; on parent

.container {
    text-align: center; /* center the child */
}
h1 {
    display: inline-flex; /* keep the background color wrapped tight */
    padding:5px;font-size:20px;background-color:green;color:#ffffff;
}

<div class="container">
  <h1>The Last Will and Testament of Eric Jones</h1>
</div>

---

Option 3

display: flex;

• requires a flex parent container

.container {
  display: flex;
  justify-content: center; /* center the child */
}
h1 {
    display: flex;
    /* margin: 0 auto; or use auto left/right margin instead of justify-content center */
    padding:5px;font-size:20px;background-color:green;color:#ffffff;
}

    <div class="container">
      <h1>The Last Will and Testament of Eric Jones</h1>
    </div>

about

Probably the most popular guide to Flexbox and one I reference constantly is at CSS Tricks

---

Option 4

display: block;

• requires a flex parent container

.container {
  display: flex;
  justify-content: center; /* centers child */
}
h1 {
    display: block;
    padding:5px;font-size:20px;background-color:green;color:#ffffff;
}

<div class="container">
  <h1>The Last Will and Testament of Eric Jones</h1>
</div>

---

Option 5

::before

• requires entering words in css file (not very practical)

h1 {
    display: flex; /* set a flex box */
    justify-content: center; /* so you can center the content like this */
}

h1::before {
    content:'The Last Will and Testament of Eric Jones'; /* the content */
    padding: 5px;font-size: 20px;background-color: green;color: #ffffff;
}

<h1></h1>

fiddle

http://jsfiddle.net/J7VBV/457/

about

More about css pseudo elements ::before and ::after at CSS Tricks and pseudo elements in general at w3schools

---

Option 6

display: inline-block;

• centering with position: absolute and translateX

• requires a position: relative parent

.container {
  position: relative; /* required for absolute positioned child */
}
h1 {
  display: inline-block; /* keeps container wrapped tight to content */
  position: absolute; /* to absolutely position element */
  top: 0;
  left: 50%; /* part1 of centering with translateX/Y */
  transform: translateX(-50%); /* part2 of centering with translateX/Y */
  white-space: nowrap; /* text lines will collapse without this */
  padding:5px;font-size:20px;background-color:green;color:#ffffff;
}

  <h1>The Last Will and Testament of Eric Jones</h1>

about

More on centering with transform: translate(); (and centering in general) in this CSS tricks article

---

Option 7

text-shadow: and box-shadow:

• not what the OP was looking for but maybe helpful to others finding their way here.

h1, h2, h3, h4, h5 {display: table;margin: 10px auto;padding: 5px;font-size: 20px;color: #ffffff;overflow:hidden;}
h1 {
    text-shadow: 0 0 5px green,0 0 5px green,
                 0 0 5px green,0 0 5px green,
                 0 0 5px green,0 0 5px green,
                 0 0 5px green,0 0 5px green;
}
h2 {
    text-shadow: -5px -5px 5px green,-5px 5px 5px green,
                  5px -5px 5px green,5px 5px 5px green;
}
h3 {
    color: hsla(0, 0%, 100%, 0.8);
    text-shadow: 0 0 10px hsla(120, 100%, 25%, 0.5),
                 0 0 10px hsla(120, 100%, 25%, 0.5),
                 0 0 10px hsla(120, 100%, 25%, 0.5),
                 0 0 5px hsla(120, 100%, 25%, 1),
                 0 0 5px hsla(120, 100%, 25%, 1),
                 0 0 5px hsla(120, 100%, 25%, 1);
}
h4 { /* overflow:hidden is the key to this one */
    text-shadow: 0px 0px 35px green,0px 0px 35px green,
                 0px 0px 35px green,0px 0px 35px green;
}
h5 { /* set the spread value to something larger than you'll need to use as I don't believe percentage values are accepted */
  box-shadow: inset 0px 0px 0px 1000px green;
}

<h1>The First Will and Testament of Eric Jones</h1>
<h2>The 2nd Will and Testament of Eric Jones</h2>
<h3>The 3rd Will and Testament of Eric Jones</h3>
<h4>The Last Will and Testament of Eric Jones</h4>
<h5>The Last Box and Shadow of Eric Jones</h5>

fiddle

https://jsfiddle.net/Hastig/t8L9Ly8o/

More Options

There are a few other ways to go about this by combining the different display options and centering methods above.

A little late to game but thought I would add my 2 cents...

To avoid adding the extra mark-up of an inner span you could change the <h1> display property from block to inline (catch is you would have ensure the elements after the <h1> are block elements.

HTML

<h1>  
The Last Will and Testament of
Eric Jones</h1> 
<p>Some other text</p>

CSS

h1{
    display:inline;
    background-color:green;
    color:#fff;
}

Result

JSFIDDLE http://jsfiddle.net/J7VBV/

As the other answers note, you can add a background-color to a <span> around your text to get this to work.

In the case where you have line-height though, you will see gaps. To fix this you can add a box-shadow with a little bit of grow to your span. You will also want box-decoration-break: clone; for FireFox to render it properly.

EDIT: If you're getting issues in IE11 with the box-shadow, try adding an outline: 1px solid [color]; as well for IE only.

Here's what it looks like in action:

.container {
  margin: 0 auto;
  width: 400px;
  padding: 10px;
  border: 1px solid black;
}

h2 {
  margin: 0;
  padding: 0;
  font-family: Verdana, sans-serif;
  text-transform: uppercase;
  line-height: 1.5;
  text-align: center;
  font-size: 40px;
}

h2 > span {
  background-color: #D32;
  color: #FFF;
  box-shadow: -10px 0px 0 7px #D32,
    10px 0px 0 7px #D32,
    0 0 0 7px #D32;
  box-decoration-break: clone;
}

<div class="container">
    <h2><span>A HEADLINE WITH BACKGROUND-COLOR PLUS BOX-SHADOW :3</span></h2>
</div>

A very simple trick to do so, is to add a <span> tag and add background color to that. It will look just the way you want it.

<h1>  
    <span>The Last Will and Testament of Eric Jones</span>
</h1> 

And CSS

h1 { text-align: center; }
h1 span { background-color: green; }

WHY?

<span> tag in an inline element tag, so it will only span over the content faking the effect.

EDIT: the answer below would apply in most cases. OP however later mentioned that they could not edit anything other than the CSS file. But will leave this here so it may be of use to others.

The main consideration that others are neglecting is that OP has stated that they cannot modify the HTML.

You can target what you need in the DOM then add classes dynamically with javascript. Then style as you need.

In an example that I made, I targeted all <p> elements with jQuery and wrapped it with a div with a class of "colored"

$( "p" ).wrap( "<div class='colored'></div>" );

Then in my CSS i targeted the <p> and gave it the background color and changed to display: inline

.colored p {
    display: inline;
    background: green;
}

By setting the display to inline you lose some of the styling that it would normally inherit. So make sure that you target the most specific element and style the container to fit the rest of your design. This is just meant as a working starting point. Use carefully. Working demo on CodePen

h1 is a block level element. You will need to use something like span instead as it is an inline level element (ie: it does not span the whole row).

In your case, I would suggest the following:

style.css

.highlight 
{
   background-color: green;
}

html

<span class="highlight">only the text will be highlighted</span>