<div class='header'>

</div>

body{
  margin: 0;
  width: 100vw;
  height: 100vh;
  display: flex;
  justify-content: center;
} 
.header{
  display: flex;
  height: 45px;
  width: 75vw;
  background: red url("https://avatanplus.com/files/resources/original/5cd1ee39d2d7216a940a9208.jpg");
  background-size: 75vw;
  background-position: top center;
  z-index: 1;
  position: relative;
  border-radius: 0 0 20px 20px;

}
.header:before {
  content:'';
  display: flex;
  height: 60px;
  width: calc( 100% - 10vw);
  background: inherit;
  background-size: inherit;
  background-position: inherit;
  z-index: -1;
  margin: 0 5vw;
  position: absolute;
  border-radius: inherit;

}