img.botao_footer_whatsapp
{
  position: fixed; 
  bottom: 20px; right: 10px; 
  z-index: 999999999999;
}

.botao_footer_whatsapp.icon_peq
   {
     display: none;
   }

   .botao_footer_whatsapp.icon_big
   {
      display: block;
   }

@media (max-width: 767px)
{
   .botao_footer_whatsapp.icon_peq
   {
     display: block !important;
     bottom: 7px; right: 17px; 
   }

   .botao_footer_whatsapp.icon_big
   {
      display: none !important;
   }

}