JSFiddle - React, Tailwind, and code Playground

HTML

<p id="toggle-sidebox">
  <i class="left">Toggle</i>
</p>

<div id="forum_box">Ads box</div>
<div id="sidebox">Sidebox</div>

CSS

#forum_box { background: red; float: left; }
#sidebox { background: blue; }

.left  { background: green;  }
.right { background: yellow; }

JavaScript

$("#toggle-sidebox").click(function(){
  if ( $('#sidebox').is(':hidden') ) {
    $('#sidebox').show();
    $('#toggle-sidebox i').toggleClass('left right');
    $("#forum_box").css({width: "33%"});
  } else {
    $('#sidebox').hide();
    $('#toggle-sidebox i').toggleClass('right left');
    $("#forum_box").css({width: "100%"});
  }
});