header { 
        display: block;
	    z-index: 2000;
        position: -webkit-sticky;
        position: -moz-sticky;
        position: -ms-sticky;
        position: -o-sticky;
        position: sticky;
        top: 0;
        height: 140px;
    }
#header {
  background-color: transparent;
  transition: all 0.3s;
}    
    
    nav {
        position: fixed;
        top: 0;
        right: 0;
        background: blue;
	    z-index: 3000;
    }
    main {
        position: relative;
        top: -140px;
        right: 0;
	    z-index: 1000;
    }

    .section-hero {
        background-image: url('/img/David.JPG');
        transform: translateY(-50%); 
        background-repeat: no-repeat;
        background-size: cover;
        height: 600px;
        color: white;
        border: 1px solid transparent; 
    }