How to write text in middle of straight line in css

h2 {
   width: 100%; 
   text-align: center; 
   border-bottom: 1px solid #000; 
   line-height: 0.1em;
   margin: 10px 0 20px; 
} 

h2 span { 
    background:#fff; 
    padding:0 10px; 
}