JSFiddle - React, Tailwind, and code Playground

HTML

<button class="pretty-button">Pretty button</button>

CSS

.pretty-button {
    border: 2px solid #333;
    background: #fff;
    padding: 5px 20px;
    position: relative;
}
.pretty-button::after {
    content: '';
    box-sizing: border-box;
    position: absolute;
    bottom: -7px;
    left: 0;
    right: 0;
    margin: 0 auto;
    border: 2px solid #333;    
    border-width: 0 0 2px 2px;
    background: #fff;
    width: 10px;
    height: 10px;
    transform: rotate(-45deg);
}