JSFiddle - React, Tailwind, and code Playground
HTML
<style rel="stylesheet">
.A { background-color: #ffff00 }
</style>
<script>
function clicked() {
console.log("color", document.getElementById("A1").style);
console.log("color", window.getComputedStyle( document.getElementById("A1") , null).getPropertyValue('background-color'));
}
</script>
</head>
<body>
<input type="button" id="A1" class="A" value="1" onclick="clicked()">