JSFiddle - React, Tailwind, and code Playground

by Rakowu

HTML

<div class="c-tab">
  <div class="mat-ink-bar"></div>
</div>

CSS

.c-tab .mat-ink-bar {
  position:relative;
  background: #3f51b5;
  height: 5px;
}

.c-tab .mat-ink-bar::after {
    content: '';
    position: absolute;
    top: 0;
    right: 0;
    left: 0;
    margin: 0 auto;
    width: 0;
    border-top: solid 50px #3f51b5;
    border-left: solid 50px transparent;
    border-right: solid 50px transparent;
}