`<head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <base href="~/" /> <link rel="stylesheet" href="@Url.Content("~/lib/bootstrap/css/bootstrap.css")" /> <link rel="stylesheet" href="@Url.Content("~/styles/theme.css")" /> <link rel="stylesheet" href="_content/Radzen.Blazor/css/default.css"> <link rel="stylesheet" href="_content/SidFormBuilder/themes.css" /> <link rel="stylesheet" href="_content/SidFormBuilder/style.css" /> <link rel="stylesheet" href="FormBuilder.Startup.styles.css" /> @RenderSection("Header", required: false) </head> in the code <link rel="stylesheet" href="_content/SidFormBuilder/themes.css" /> <link rel="stylesheet" href="FormBuilder.Startup.styles.css" /> ` is not exists !!!!!