关于link, visited, hover, active

      
        1
      
      
        #navbar:active, #backbtn:active 
      
      {


      
        2
      
      
            background-color
      
      :
      
         #005801
      
      ;


      
        3
      
       }
    

      
        #navbar:hover,#navbar:active,  #backbtn:hover，#backbtn:active 
      
      {
      
        

    background-color
      
      :
      
         #005801
      
      ;

}