index.html
<body>
<header class="header">
</header>
</body>
styles.css
/* Basic reset of each and every element */
*,
*::after,
*::before {
margin: 0;
padding: 0;
box-sizing: border-box;
}
.header {
height: 20vh;
background-image:
linear-gradient(
to right bottom,
rgba(126, 213, 111, 0.4),
rgba(40, 180, 131, 0.4)),
url('../img/pixabay_waves-g9a31aaaec_640.jpg');
background-size: cover;
background-position: center;
}