Here’s the problem. You’ve got this hardcoded in your stylesheet for Slick Side menu in vc_slidemenustyle.css

/* -----------------------------------------------------------------------------

  SLIDE AND PUSH MENUS COMPONENT
  
----------------------------------------------------------------------------- */
/**
 * Menu overview.
 */
.c-menu {
  position: fixed;
  z-index: 999999;
  background-color: #67b5d1;
  -webkit-transition: -webkit-transform 0.3s;
          transition: transform 0.3s;
}