JSFiddle - React, Tailwind, and code Playground

by Elena Shevchuk

HTML

<div class="a">
    <div class="b"></div>
</div>

CSS

.a {
    width: 300px;
    height: 100px;
    background: radial-gradient(100% 100% at 50% 40%, #1e5799 53%,#7db9e8 54%);
    border: 2px solid black;
    position: relative;
    
}
.b {
    position: absolute;
    width: 20px;
    height: 20px;
    border: 2px solid black;
    border-left: none;
    border-bottom: none;
    left: 100%;
    top: 50%;
    margin-top: -10px;
    margin-left: -10px;
    overflow: hidden;
    -webkit-transform: rotate(45deg);
}
.b:before {
    position: absolute;
    content: "";
    width: 300px;
    height: 100px;
    left: 62px;
    top: 96px;
    margin-top: -49px;
    -webkit-transform: rotate(-45deg);    
    margin-left: -300px;
    background: radial-gradient(100% 100% at 47% 40%, #1e5799 53%,#7db9e8 54%);
}