鼠标经过时背景变色的效果(小技巧)

< style  type ="text/css" >
.cl1  {
    background :  olive
}
.cl2  {
    background :  white
     }

    
}
</ style >
< body >
< table >
               < tr  onMouseover ="this.className='cl1';"  onMouseout ="this.className='cl2'" >  
                 < td > aa </ td >
                 < td > bb </ td >
</ tr >
   < tr  onMouseover ="this.className='cl1';"  onMouseout ="this.className='cl2'" >  
                 < td > aa </ td >
                 < td > bb </ td >
</ tr >
   < tr  onMouseover ="this.className='cl1';"  onMouseout ="this.className='cl2'" >  
                 < td > aa </ td >
                 < td > bb </ td >
</ tr >
   < tr  onMouseover ="this.className='cl1';"  onMouseout ="this.className='cl2'" >  
                 < td > aa </ td >
                 < td > bb </ td >
</ tr >

</ table >
</ body >