background-image: linear-gradient(to top, rgb(207, 207, 213) 0%, rgb(135, 129, 129) 50%, rgb(207, 207, 213) 100%);
<div class="triangle-right"></div>
.triangle-right {
border-image: none;
height: 30px;
width: 150px;
background-image: linear-gradient(to top, rgb(207, 207, 213) 0%, rgb(135, 129, 129) 50%, rgb(207, 207, 213) 100%);
}
.triangle-right:after{
content:"";
display: block;
height: 0;
border-left:20px solid black;
border-top:15px solid transparent;
border-bottom:15px solid transparent;
}