JSFiddle - React, Tailwind, and code Playground

HTML

<div class="input-container">
    <input type="text"/>
</div>

CSS

.input-container {
    position: relative;
    float: left;
}

.input-container:after {
    position: absolute;
    right: 0;
    top: 0;
    content: '@gmail.com';
}