HTML - 边界问题

Question

我有一个嵌套表：

    <table style="height: 100%; width: 100%; position: fixed; top: 0; left: 0; border-collapse: collapse" cellpadding="0"
           cellspacing="0" border="0">
        <tr>
            <td colspan="3" style="height: 47%; background-color: #000000; opacity: 0.35; filter: alpha(opacity=35);" />
        </tr>
        <tr>
            <td style="height: 6%; width: 40%; background-color: #000000; opacity: 0.35; filter: alpha(opacity=35);" nowrap />
            <td style="height: 6%; background-color: White;">
                <table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse">
                    <tr>
                        <td valign="middle" >
                            <img src="~/images/loading.gif" align="middle" />
                        </td>
                        <td valign="middle">
                            <b>Please wait... </b>
                        </td>
                    </tr>
                </table>
            </td>
            <td style="height: 6%; width: 40%; background-color: #000000; opacity: 0.35; filter: alpha(opacity=35);" />
        </tr>
        <tr>
            <td colspan="3" style="height: 47%; background-color: #000000; opacity: 0.35; filter: alpha(opacity=35);" />
        </tr>
    </table>

我的问题在于嵌套表：边框出现，即使它被设置为零。为什么？

以下是它的外观：

如何摆脱边界？