搜索框设置背景图 通过设置placeholder属性添加

/#keyword/id名为keyword的input框（搜索框）添加背景图片
#keyword::-webkit-input-placeholder {
color: transparent;
text-indent: -9999px;
background: transparent url(../img/google_custom_search_watermark.gif) no-repeat 10% center;
}
#keyword::-moz-placeholder {
/* Firefox 19+ */
color: transparent;
text-indent: -9999px;
background: #fff url(../img/google_custom_search_watermark.gif) no-repeat 10% center;
}
#keyword:-moz-placeholder {
/* Firefox 18- */
color: transparent;
text-indent: -9999px;
background: transparent url(../img/google_custom_search_watermark.gif) no-repeat 10% center;
}
#keyword:-ms-input-placeholder {
/* IE 10- */
color: transparent;
text-indent: -9999px;
background: transparent url(../img/google_custom_search_watermark.gif) no-repeat 10% center;
}