Adam Klimowski

Try to add this to your sidebar-login.js file:

$(document).ready(function(){
  $('form').find('input[name="log"]').each(function(ev)
  {
      if(!$(this).val()) {
     $(this).attr("placeholder", "Username");
  }
  });
});

$(document).ready(function(){
  $('form').find('input[name="pwd"]').each(function(ev)
  {
      if(!$(this).val()) {
     $(this).attr("placeholder", "Password");
  }
  });
});