JSFiddle - React, Tailwind, and code Playground

HTML

<div class="green">
    <div class="left"></div>
</div>

<div class="green">
    <div class="right"></div>
</div>

CSS

.green {
    background-color: green;
    width: 30px;
    height: 30px;
    position: relative;
}
.green > .left {
    background-color: #fff;
    height: 35px;
    width: 30px;
    position: absolute;
    right: 0;
    bottom: 0;
    border-radius: 100% 0 0 0;
}

.green > .right {
    background-color: #fff;
    height: 35px;
    width: 30px;
    position: absolute;
    left: 0;
    bottom: 0;
    border-radius: 0 100% 0 0;
}