section {
   width: 50%;
   margin: 0 auto;
}
h2 {
   position: relative;
   background: black;
}
h2:before, h2:after {
   content: "";
   position: absolute;
   background: black;  /* Match the background */
   top: 0;
   bottom: 0;
   width: 9999px;   /* some huge width */
}
h2:before {
   right: 100%;
}
h2:after {
   left: 100%;
}