JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="dark"><a rel="25" class="0725" style="color: rgb(255, 255, 255);">25</a></li>
    <li class="dark"><a rel="26" class="0726" style="color: rgb(255, 255, 255);">26</a></li>
    <li class="dark"><a rel="27" class="0727" style="color: rgb(255, 255, 255);">27</a></li>
    <li class="dark"><a rel="28" class="0728" style="color: rgb(255, 255, 255);">28</a></li>
    <li class="dark"><a rel="29" class="0729" style="color: rgb(255, 255, 255);">29</a></li>
    <li class="dark"><a rel="30" class="0730" style="color: rgb(255, 255, 255);">30</a></li>
    <li class="dark first"><a rel="31" class="0731" style="color: rgb(255, 255, 255);">31</a></li>
    <li class="dark"><a rel="1" class="0801" style="color: rgb(255, 255, 255);">1</a></li>
    <li class="dark"><a rel="2" class="0802" style="color: rgb(255, 255, 255);">2</a></li>
    <li class="dark"><a rel="3" class="0803" style="color: rgb(255, 255, 255);">3</a></li>
    <li class="dark"><a rel="4" class="0804" style="color: rgb(255, 255, 255);">4</a></li>
    <li class="dark"><a rel="5" class="0805" style="color: rgb(255, 255, 255);">5</a></li>
    <li class="dark"><a rel="6" class="0806" style="color: rgb(255, 255, 255);">6</a></li>
    <li class="dark"><a rel="7" class="0807" style="color: rgb(255, 255, 255);">7</a></li>
    <li class="dark"><a rel="8" class="0808" style="color: rgb(255, 255, 255);">8</a></li>
    <li class="dark"><a rel="9" class="0809" style="color: rgb(255, 255, 255);">9</a></li>
    <li class="dark"><a rel="10" class="0810" style="color: rgb(255, 255, 255);">10</a></li>
    <li class="dark"><a rel="11" class="0811" style="color: rgb(255, 255, 255);">11</a></li>
    <li class="dark"><a rel="12" class="0812" style="color: rgb(255, 255, 255);">12</a></li>
</ul>

JavaScript

var today = new Date();
var tdd = zeroPad(today.getDate(),2);
var tmm = zeroPad(today.getMonth()+1,2);

var yesterday = new Date();
yesterday.setDate(today.getDate() - 1);
var ydd = zeroPad(yesterday.getDate(),2);
var ymm = zeroPad(yesterday.getMonth()+1,2);

$('.'+tmm + tdd).css('background-color','red');
$('.'+ymm + ydd).css('background-color','blue');

function zeroPad(num, places) {
  var zero = places - num.toString().length + 1;
  return Array(+(zero > 0 && zero)).join("0") + num;
}