How I can add Costume CSS on ASP

Question is like this I have ASPxGridView and I can't use Costume CSS and question is how it is working How ASPxGridView can Get Costume CSS style?

<pre lang="HTML">
dx:ASPxGridView ID="ASPxGridView1" CssClass="mGrid" PagerStyle-CssClass="pgr" AlternatingRowStyle-CssClass="alt" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" KeyFieldName="ID" >
<columns> <dx:gridviewdatatextcolumn fieldname="ID" readonly="True" visibleindex="0">
<editformsettings visible="False">

<dx:gridviewdatatextcolumn fieldname="FIRST_NAME" visibleindex="1">

<dx:gridviewdatatextcolumn fieldname="LAST_NAME" visibleindex="2">

<dx:gridviewdatatextcolumn fieldname="Alt_Firstname" visibleindex="3">

<dx:gridviewdatatextcolumn fieldname="Alt_Suranme" visibleindex="4">

<dx:gridviewdatatextcolumn fieldname="CO_ID" visibleindex="5">

<dx:gridviewdatatextcolumn fieldname="CO_NAME" visibleindex="6">

<dx:gridviewdatatextcolumn fieldname="PHONE_WORK" visibleindex="7">

<dx:gridviewdatatextcolumn fieldname="PHONE_HOME" visibleindex="8">

<dx:gridviewdatatextcolumn fieldname="MOBILE" visibleindex="9">

<dx:gridviewdatatextcolumn fieldname="FAX" visibleindex="10">

<dx:gridviewdatatextcolumn fieldname="EMAIL" visibleindex="11">

<dx:gridviewdatadatecolumn fieldname="BirthDay" visibleindex="12">

<dx:gridviewdatatextcolumn fieldname="Group_ID" visibleindex="13">

<dx:gridviewdatatextcolumn fieldname="Note" visibleindex="14">

<dx:gridviewdatadatecolumn fieldname="Date_Modified" visibleindex="15">

<dx:gridviewdatatextcolumn fieldname="Position" visibleindex="16">

<dx:gridviewdatatextcolumn fieldname="Author" visibleindex="17">

<settings showfilterrow="True"></pre>

.mGrid {
width: 100%;
background-color: #fff;
margin: 25px 0 10px 0;
border: solid 1px #f1b206;
border-collapse:collapse;
}
.mGrid td {
padding: 2px;
border: solid 1px #c1c1c1;
color: #717171;
}
.mGrid th {
padding: 4px 2px;
color: #fff;
background: #424242 url(grd_head.png) repeat-x top;
border-left: solid 1px #525252;
font-size: 0.9em;
}
.mGrid .alt { background: #fcfcfc url(grd_alt.png) repeat-x top; }
.mGrid .pgr { background: #424242 url(grd_pgr.png) repeat-x top; }
.mGrid .pgr table { margin: 5px 0; }
.mGrid .pgr td {
border-width: 0;
padding: 0 6px;
border-left: solid 1px #666;
font-weight: bold;
color: #fff;
line-height: 12px;
}
.mGrid .pgr a { color: #666; text-decoration: none; }
.mGrid .pgr a:hover { color: #000; text-decoration: none; }



but it's not working it isn't showing full cod :((