Responsive Left Sidebar Open Close

I have one question about responsive left sidebar open close function. I have created this DEMO from codepen.io You can see in the demo there is a button (Click to show blue div).

Solution 1:

The problem is with CSS, replace media query css with this CSS:

@media all and (max-width: 840px) {
  .left {
     z-index: 9999999999999 !important;
  }
  .secret {
    float: left;
    display: block;
  }

  .click_open_close {
    display: block;
  }
}