Besides allowing any kind of background, my solution doesn’t add any extra HTML tag and scales with every size of text.
h1 {
overflow: hidden;
text-align: center;
}
h1:before,
h1:after {
background-color: #000;
content: "";
display: inline-block;
height: 1px;
position: relative;
vertical-align: middle;
width: 50%;
}
h1:before {
right: 0.5em;
margin-left: -50%;
}
h1:after {
left: 0.5em;
margin-right: -50%;
}