JSFiddle - React, Tailwind, and code Playground

HTML

<div class="row">
    <div class="col-lg-4">
        <label for="email">E-Mail ID:</label>
    </div>
    <div class="col-lg-8 input-group" style="width:50%">
        <input type="text" id="userEmail" class="form-control" name="email" required /> <span class="input-group-addon">@gmail.com</span>

        <hr/>
    </div>
</div>

CSS

.input-group-addon {
    margin-left: -90px;
    color: #666;
}
#userEmail {
    padding-right: 85px;
}