JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" placeholder="some cool text"/>

CSS

input[type=text]:-moz-placeholder {
    color: #000;
    transition: color 1s;
}

input[type=text]:focus:-moz-placeholder {
    color: #aaa;
}

input[type=text]::-webkit-input-placeholder {
    color: #000;
    transition: color 1s;
}

input[type=text]:focus::-webkit-input-placeholder {
    color: #aaa;
}