html, body {
    width: 100%;
    height: 100%;
}

.bg {
  /* The image used */
  background-image: url("../img/bg_pic_30.jpg");

  /* Full height */
  height: 100%;

  /* Center and scale the image nicely */
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}

.demo-wrap {
    overflow: hidden;
    position: relative;
  }
  
  .demo-bg {
    opacity: 0.2;
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: auto;
  }
  
  .demo-content {
    position: relative;
  }