Untitled

body{
    background-color:#f4f4f4;
    color:#555;
    font-family:sans-serif;
    font-size:16px;
    line-height:1.6em;
    margin:0;
}

.container{
    width:80%;
    margin:auto;
    overflow:hidden;
}

#main-header{
    background-color:coral;
    color:#fff;
}

<!DOCTYPE html>
<html>
<head>
    <title>My Website</title>
    <link rel="stylesheet" type="text/css" href="style1.css">
</head>
<body>
    <header id="main-header">
        <div class="container">
            <h1>My Website</h1>
        </div>
</body>
</html>