JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" placeholder="Hello"></input>
<input type="text" class="other" placeholder="Hello"></input>

CSS

::-webkit-input-placeholder { font-size: 16pt; color: #555; }
::-moz-placeholder { font-size: 16pt; color: #555; }
:-ms-input-placeholder { font-size: 16pt; color: #555; }
input:-moz-placeholder { font-size: 16pt; color: #555; }

.other::-webkit-input-placeholder { font-size: 12pt; color: red; }
.other::-moz-placeholder { font-size: 12pt; color: red; }
.other:-ms-input-placeholder { font-size: 12pt; color: red; }
input.other:-moz-placeholder { font-size: 12pt; color: red; }