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.dark-overlay {
    background-color: rgba(0,0,0,0.7);
    top:0;
    left:0;
    width: 100%;
    height: 100vh;
  }

section#section-showcase>.dark-overlay>.showcase-inner>.container>.row>.col

#section-showcase{
  background-image:url('../img/bg.jpg');
  background-size:cover;
  background-position:center;
  height:100vh; /*vw is an option too*/
}