.main
position: relative
background-image: linear-gradient(-130deg, #790504 0%, #db0a07 100%)
svg
position: absolute
bottom: 0
left: 0
width: 100%
height: 15vw
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="none">
<polygon fill="white" points="0,100 100,0 100,100"/>
</svg>