Weird behavior in asp.net - asp.net

Question

Can someone tell one why do i get the blue line that i show here: (and also it is really a good practice to define a class for just text-align:center instead of inline code?)
Code:
<asp:Panel ID="PnlBarraFinalizarMostrar" runat="server" CssClass="izq">
<asp:LinkButton ID="LkBRegresar" runat="server" CssClass="LKBPequeño" OnClick="LkBRegresar_Click">Regresar</asp:LinkButton>
</asp:Panel>
<%--alumn's info--%>
<asp:Panel ID="PnlAlumno" runat="server" BackColor="Yellow">
<table runat="server" class="datos" style="background-color:Green;">
<tr>
<td rowspan="4" style="width: 65px;">
<asp:Image ID="ImgAlumno" runat="server" BorderWidth="0px"
Width="62.7" Height="84" />
</td>
<td style="width: 75px;">
Alumno:
</td>
<td style="width:225px; white-space:nowrap;">
<asp:Label ID="LbDAlumno" runat="server" />
</td>
<td style="width: 40px;">
Ciclo:
</td>
<td>
<asp:Label ID="LbDciclo" runat="server" />
</td>
</tr>
<tr>
<td>
Carrera:
</td>
<td>
<asp:Label ID="LbDCarrera" runat="server" />
</td>
<td>
Plan:
</td>
<td>
<asp:Label ID="LbDPlan" runat="server" />
</td>
</tr>
<tr>
<td>
Maximo UV:
</td>
<td>
<asp:Label ID="LbDMaximoUV" runat="server" />
</td>
<td>
CUM:
</td>
<td>
<asp:Label ID="LbDCum" runat="server" />
</td>
</tr>
<tr style="vertical-align: text-top; background-color:Gray;">
<td>
UV Inscritas:
</td>
<td>
<asp:Label ID="LbDUVInscritas" runat="server" />
</td>
<td>
Avance:
</td>
<td>
<asp:Label ID="LbDAvance" runat="server" />
</td>
</tr>
</table>
</asp:Panel>
<br />
<%--Detalle de Asignaturas--%>
<asp:Panel ID="PnlHojaAsesoriaCursosInscritos" runat="server" Width="100%" BackColor="Sienna">
<table class="encabezado">
<tr>
<td>
<asp:Label ID="lbTituloHAsesoriaCInscritos" runat="server" Text="Hoja Asesoria o Cursos Inscritos" />
</td>
</tr>
</table>
<table id="THojaA" runat="server" class="tabla" style="padding:0px;background-color:Red;">
...
encabezado.css (header)
.encabezado
{
font-size:10pt;
text-align:left;
background-color:#152B81; color:#FFFFFF;
border-spacing: 2px;
padding:3px 4px 2px 5px;
width:100%;
}
datos.css (data)
.datos
{
font-size: 9pt;
border: 1px solid #152B81;
background-color: #DBE7F6;
color: #152B81;
width: 100%;
text-align: left;
border-spacing:0px;
padding:4px 4px 4px 5px;
}
after using inspection i detect a border-bottom!:
inspector:

Answer 1

Use inspect element to check what is happening once the code is parsed. or you can post the parsed html here.