判断表单不能为空（表格形式的）
<style>
td:last-child{color: red; font-weight: bold;}
</style>
<table cellpadding="10" border="1px solid #ddd">
<tr>
<td>账号:</td>
<td><input >
<style>
td:last-child{color: red; font-weight: bold;}
</style>
<table cellpadding="10" border="1px solid #ddd">
<tr>
<td>账号:</td>
<td><input >