Full Browser Width Bars

HTML

<section>
    <h2>test</h2>
    <p>text</p>
    <h2>test</h2>
    <p>text</p>

</section>

CSS

* {
    margin: 0;
    padding: 0;
}

body, html {
    margin: 0;
    padding: 0;
    line-height: 1;
}

section {
    width:50%;
    min-width: 500px;
    margin: 0 auto;
}

h2 {
    background: red;
    height: 30px;
}

h2:before{
    width: 100%;
    height: inherit;
    display: block;
    background: blue;
    content: "";
    position: absolute;
    left: 0;
    z-index: -1;
}