JSFiddle - React, Tailwind, and code Playground

HTML

<form action="#" method="post">
    <fieldset>
        <input type="text" name="something" id="something" />
        <button>It's a button!</button>
    </fieldset>
</form>

CSS

fieldset {
    font-size: 1em;
    padding: 0.5em;
    border-radius: 1em;
    font-family: sans-serif;
    border-width: 0;
}
label, input, button {
    font-size: inherit;
    padding: 0.3em 0.4em;
    margin: 0.1em 0.2em;
    border: 1px solid #f90;
    background-color: #fff;
    float: left;
    -webkit-box-sizing:border-box;
    -moz-box-sizing:border-box;
    box-sizing:border-box;
    height: 33px;
}
input {
    margin-right: 0;
    border-radius: 0.6em 0 0 0.6em;
}
input:focus {
    outline: none;
    background-color: #ffa;
    background-color: rgba(255, 255, 210, 0.5);
}
button {
    margin-left: 0;
    border-radius: 0 0.6em 0.6em 0;
    background-color: #aef;
}
button:active, button:focus {
    background-color: #acf;
    outline: none;
}