css in c# style update after click button

in first time that i insert to page it is like: enter image description here

then after click on one of them it is like: enter image description here

How do I make the first CSS file load? i try to write thet in css file and this not change so now i use in this code: style type="text/css" css:

nav > ul {

height: 4.10em;
background-image:url(images/Untitled-1.jpg);
ackground-color:#000053;

nav > ul > li {

float: right;

nav > ul > li:not( :last-child ) > a {

border-right: 1px solid #fcd4ec !important;/*between*/

nav > ul > li:hover > a, #nav > ul:not( :hover ) > li.active > a {

background-color: #fff;/*ul li out*/
color:#2187cb;

in c#:

    <li dir="rtl"><a href='#' dir="rtl" >
                    <asp:LinkButton ID="LinkButton6" runat="server" dir="rtl" OnClick="Home_Click" Font-Size="20"  Font-Names="Suez One,sans-serif" Width="75px" >ראשי</asp:LinkButton>
                </a></li>

`