JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="inner-triangle"></div>
    <div class="outer-triangle"></div>
</div>

CSS

.container{
    border: 2px solid gray;
    position: relative;
    height: 100px;
    width: 100px;
}

.inner-triangle{
    border-left: 20px solid transparent;
    border-right: 20px solid green;
    border-bottom: 20px solid transparent;
    height: 0;
    width: 0;
    position: absolute;
    right: 0px;
    z-index: 2;
}

.outer-triangle{
    border-left: 24px solid transparent;
    border-right: 24px solid gray;
    border-bottom: 24px solid transparent;
    height: 0;
    width: 0;
    position: absolute;
    right: 0px;
    z-index: 1;
}