JSFiddle - React, Tailwind, and code Playground

HTML

<div class="Div1">Div1</div>
<div class="Div2">Div2</div>

CSS

.Div1{width:100px; height:100px; background-color:red; float:left; margin-right:30px; }
.Div2{width:100px; height:100px; background-color:#00C; float:left }

JavaScript

var defaultBackground = $(".Div1").css("background-color");
$( ".Div2" )
  .mouseover(function() {
      $(".Div1").css("background-color", "yellow");
  })
  .mouseout(function() {
    $(".Div1").css("background-color", defaultBackground);
  });