JSFiddle - React, Tailwind, and code Playground

HTML

<input id="emailField" type="text" placeholder="Email or phone" /><br />

CSS

#emailField {
                width: 100%;
                font-family: Roboto,RobotoDraft,Helvetica,Arial,sans-serif;
                font-size: 14px;
                border: none;
                border-bottom: 1px solid lightgrey;
                color: grey;
            }
            #emailField:focus {
                position:absolute;
                font-size: 11px;
                width: 82%;
                top: 1em;
            }