JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="seasons">
  <li id="winter"class="winter"><a data-season="winter" href="#">Зима</a></li>
  <li class="spring"><a data-season="spring" href="#">Весна</a></li>
  <li class="summer"><a data-season="summer" href="#">Лето</a></li>
  <li class="autumn"><a data-season="autumn" href="#">Осень</a></li>
</ul>

CSS

.active,.active a {
  color: red;
}

JavaScript

var d = new Date();
var n = d.getMonth();

switch (n) {
  case 0:
  case 1:
  case 11:
    alert( 'Зима' );
    var winter = document.getElementById("winter");
		winter.className += " active";
    break;
  case 2:
  case 3:
  case 4:
  case 5:
    alert( 'Весна!' );
    break;
}