css 背景透明 实现代码

效果预览:css: [code] 1: <style type="text/css"> 2: <!-- 3: body{ 4: margin:0; 5: padding:0; 6: background-color:#FFFFFF; 7: } 8: .alpha1,.alpha2{ 9: width:100%; 10: height:auto; 11: min-height:250px;/* 必需 */ 12: