大家来看看我的这个代码为什么显示不出来框啊？
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Test</title><style type="text/css">.1{background-color:#F00;width:100px;height:100px;float:left}.2{background-color:#0F0;width:200px;height:200px;float:left}.3{background-color:#0F0;width:50px;height:50px;float:left;clear:left}</style></head><body><div class="1"></div><div class="2"></div><div class="3"></div></body></html>