Most of the tools in those interfaces are either legacy and still done using WebForms. It's on the roadmap for Episerver at the partner event last week that we're finally moving to .NET Core 3.0 so everything will change but if your using razor files as we are for the admin plugins you've just got to render them yourself.

You can extract the CMS.zip file in the modules folder if you want to see examples of the WebForm markup. Here for example in the Edit Security control EditSecurity.aspx

<asp:Content ContentPlaceHolderID="MainRegion" runat="server">
    <br />
    <EPiServerUI:ToolButton ID="SaveButton" IsDialogButton="True" Enabled="false" DisablePageLeaveCheck="true" OnClick="SaveButton_Click" OnClientClick="onClick();" runat="server" Text="<%$ Resources: EPiServer, button.save %>" ToolTip="<%$ Resources: EPiServer, button.save %>" SkinID="Save" />
    <EPiServerUI:ToolButton id="UserGroupAddButton" IsDialogButton="False" GeneratesPostBack="False" OnClientClick="OpenUserGroupBrowser(0);" runat="server"  Text="<%$ Resources: EPiServer, button.addusergroupsid %>" ToolTip="<%$ Resources: EPiServer, button.addusergroupsid %>" SkinID="AddUserGroup" />
    <br />
    <br />
    <EPiServerUI:MembershipAccessLevel CssClass="EPEdit-sidAccessLevel" SaveButtonID="SaveButton"  ID="sidList" runat="server" />
    <br />
      <div class="epi-formArea">
        <div class="epi-size25">
            <div>
                <asp:CheckBox runat="server" ID="IsInherited" onClick="setInputStatus();" Text="<%$ Resources: EPiServer, admin.security.inherit %>" ToolTip="<%$ Resources: EPiServer, admin.security.inheritinfo %>" cssclass="epiinheritaccess" /><br />
            </div>
        </div>
    </div>
    <hr />

    <EPiServer:Translate Text="#user" ID="RoleInfo" runat="server" />
    <ul>
        <asp:Repeater ID="ListRoles" runat="server">
            <ItemTemplate>
                <li>
                    <%# System.Web.HttpUtility.HtmlEncode(Container.DataItem.ToString()) %>
                </li>
            </ItemTemplate>
        </asp:Repeater>
    </ul>
<EPiServerScript:ScriptEvent ID="initScript" runat="server" EventType="load" EventTargetClientNode="window" EventHandler="setInputStatus" />
<EPiServerScript:ScriptEvent ID="ScriptEvent1" runat="server" EventType="load" EventTargetClientNode="window" EventHandler="StoreInitialAccessRights" />
</asp:Content>

As you can see they have WebForm controls but the same doesn't exist for Razor when working with the admin area that's more legacy.

Hope that helps