JSFiddle - React, Tailwind, and code Playground

HTML

<div class='menu'>
<a href='#'>Item 1</a>
<a href='#'>Item 2</a>
</div>

CSS

.menu {
    padding: 0 10px;
}
.menu a {
    display: inline-block;
    background: black;
    color: white;
    z-index: 2;
    padding: 0 10px;
    height: 30px;
    line-height: 30px;
    margin: 0 15px;
    position: relative;
}

.menu a:after {
    display: block;
    content: ' ';
    position: absolute;
    top: 0;
    right: -30px;
    z-index: -1;
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 30px 30px 0 30px;
    border-color: black transparent transparent transparent;
}

.menu a:before {
    display: block;
    content: ' ';
    position: absolute;
    top: 0;
    left: -30px;
    z-index: -1;
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 0 30px 30px 30px;
    border-color: transparent transparent black transparent;
}

.menu a:hover {
    background: red;
}

.menu a:hover:before{
    border-bottom-color: red;
}

.menu a:hover:after {
    border-top-color: red;
}