JSFiddle - React, Tailwind, and code Playground

HTML

<textarea name="" id="" placeholder="Пишите нам ..."></textarea>

CSS

textarea{
    height: 30px;
    width: 400px;
    overflow: hidden;
    -webkit-transition: height .5s ease-in;
    transition: height .5s ease-in;
}
textarea:focus{
    height: 100px;
    overflow: auto;
}