TabPanel具有height和width属性.用px
给他们分配数值

TabPanels have height and width properties. Assign them the numeric values with px

<ajaxtoolkit:tabcontainer runat="server" xmlns:ajaxtoolkit="#unknown">
        OnClientActiveTabChanged="ClientFunction" 
        Height="150px"
        Width="400px"
        ActiveTabIndex="1"        
        OnDemand="true"        
        AutoPostBack="false"
        TabStripPlacement="Top"
        CssClass="ajax__tab_xp"
        ScrollBars="None"
        UseVerticalStripPlacement="true"
        VerticalStripWidth="120px"
        >
    <ajaxtoolkit:tabpanel runat="server">
        HeaderText="Signature and Bio"
        Enabled="true"
        ScrollBars="Auto"        
        OnDemandMode="Once"
        <contenttemplate>
            ...
        </contenttemplate>
    />
</ajaxtoolkit:tabpanel></ajaxtoolkit:tabcontainer>