One option is to put a container that gives the size to the div with the clip, give the internal div 100% wide and high, and the image make it cover the entire background:
<!DOCTYPE html>
<html>
<head>
<style type="text/css">
body {
padding: 0;
margin: 0;
}
#caja-contenedor {
width: 100vw;
height: 100vh;
}
#caja1 {
background-position: center;
background-repeat: no-repeat;
background-image: url(https://images.unsplash.com/photo-1517880014665-8b84b2e26002?ixlib=rb-0.3.5…jEyMDd9&s=f68dce4…&auto=format&fit=crop&w=500&q=60);
-webkit-clip-path: polygon(0 1%, 100% 0%, 100% 70%, 0% 90%);
clip-path: polygon(0 1%, 100% 0%, 100% 70%, 0% 90%);
width: 100%;
height: 100%;
background-size: cover;
}
</style>
</head>
<body>
<div id="caja-contenedor">
<div id="caja1">
fondo marino
</div>
</div>
</body>
</html>
-
#caja-contenedor
dictates the size
-
#caja1
adapts to clip and background
edit I add demo changing id by classes and an example of how to limit the width or height of the container
#caja-contenedor {
width: 100vw;
height: 100vh;
max-width: 640px;
max-height: 800px;
margin: 0 auto;
}
.contenedor {
position: relative;
}
.caja-bkg {
background-position: center;
background-repeat: no-repeat;
background-image: url(https://images.unsplash.com/photo-1517880014665-8b84b2e26002?ixlib=rb-0.3.5…jEyMDd9&s=f68dce4…&auto=format&fit=crop&w=500&q=60);
-webkit-clip-path: polygon(0 1%, 100% 0%, 100% 70%, 0% 90%);
clip-path: polygon(0 1%, 100% 0%, 100% 70%, 0% 90%);
background-size: cover;
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
color: #fff;
}
.row {
width: 100%;
}
.col-20 {
width: 20%;
}
.col-60 {
width: 60%;
}
.unatabla {
display: flex;
flex-direction: row;
min-height: 320px;
}
<div id="caja-contenedor" class="contenedor">
<div class="caja-bkg">
fondo marino
</div>
</div>
<div class="row unatabla">
<div class="col-20">primera columna</div>
<div class="col-60 contenedor">
<div class="caja-bkg">
fondo marino 2
</div>
</div>
<div class="col-20">tercera columna bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla </div>
</div>