Tab border - Changing yellow to blue

Does anyone know how I can change the top border on the active and non active tabs to be blue rather than the default yellow? Also occurs when you hover over a tab.

<act:TabContainer runat="server" ID="Tabs" ActiveTabIndex="0" Height="440px"><act:TabPanel runat="server" ID="tpDetails" HeaderText="Details"><ContentTemplate>
                                            Test</ContentTemplate></act:TabPanel><act:TabPanel runat="server" ID="tpHistory" HeaderText="History"><ContentTemplate>
                                            Test</ContentTemplate></act:TabPanel><act:TabPanel runat="server" ID="tpAlerts" HeaderText="Alerts"><ContentTemplate>
                                            Test</ContentTemplate></act:TabPanel></act:TabContainer></div>

Thanks