为什么jquery-ui对话框的高度总是设置为auto？

Here is the dialog html:

这是对话框html：

<div id="login-prompt">
    Please @Html.ActionLink("Log on", "LogOn", "Account", new { returnUrl = Request.RawUrl }, null) 
    or @Html.ActionLink("Register", "Register", "Account", new { returnUrl = Request.RawUrl }, null)
</div>
<div id