JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
  <p>Enter code:</p>
  <form id="access">
    <input placeholder="code" id="access-code" name="access-code" type="text" tabindex="1" required>
  </form>
</div>

CSS

#wrapper {
    display: inline-flex;
    align-items: center;
    justify-content: flex-start;
    position: absolute;
    top: 0;
    left: 0;
    text-align: left;
    vertical-align: top;
    border: 1px solid #000;
    margin: 0;
    padding: 0;
}
#wrapper p {
    font-size: 16px;
    text-transform: uppercase;
    background-color: rgba(255, 255, 255, 0.5);
    padding: 0.5em 1em;
    cursor: pointer;
}
#wrapper:hover form#access {
    width: 100px;
}
form#access {
    width: 0%;
    margin: 0;
    padding: 0;
    overflow:hidden;
    -webkit-transition: width 1s ease-in-out;
    -moz-transition: width 1s ease-in-out;
    -o-transition: width 1s ease-in-out;
    transition: width 1s ease-in-out;
}
form#access input {
    font-size: 18px;
    display: inline-block;
    vertical-align: top;
    padding: 0;
    margin: 0;
    border: none;
    max-width: 100px;
}