function expandbanner(){
  this.floatBan=document.getElementById("floatBan");
  this.floatBan.style.width = '800px';
  this.floatBan.style.height= '500px';
  this.floatBan.style.overflow= "hidden";
}

function contractbanner(){
  this.floatBan=document.getElementById("floatBan");
  this.floatBan.style.width = '100px';
  this.floatBan.style.height= '200px';
  this.floatBan.style.overflow= "hidden";
}