@page "/" <h1>Hello, world!</h1> Welcome to your new app. <Alert @ref="alert" /> <button @onclick="(() => alert.Show())">Show using ref</button> @code { Alert alert; }
namespace BlazorFiddleProject { using Microsoft.AspNetCore.Components.Builder; using Microsoft.Extensions.DependencyInjection; public class Startup { public void ConfigureServices(IServiceCollection services) { } public void Configure(IComponentsApplicationBuilder app) { app.AddComponent<App>("app"); } } }
<!DOCTYPE html> <html> <head> <meta charset="utf-8"/> <meta name="viewport" content="width=device-width"> <title>BlazorFiddleProject</title> <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous"> <style> .alert { position: fixed; left: 0; top: 0; width: 100%; height: 100%; background-color: rgba(0, 0, 0, 0.5); opacity: 0; visibility: hidden; transform: scale(1.1); transition: visibility 0s linear 0.25s, opacity 0.25s 0s, transform 0.25s; } .alert-content { position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); background-color: white; padding: 1rem 1.5rem; width: 24rem; border-radius: 0.5rem; } .alert-close-button { float: right; width: 1.5rem; line-height: 1.5rem; text-align: center; cursor: pointer; border-radius: 0.25rem; background-color: lightgray; } .alert-close-button:hover { background-color: darkgray; } .alert-show { opacity: 1; visibility: visible; transform: scale(1.0); transition: visibility 0s linear 0s, opacity 0.25s 0s, transform 0.25s; } </style> <script type="text/javascript"> </script> </head> <body> <app>Loading...</app> <script src="_framework/blazor.webassembly.js"></script> <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script> </body> </html>

Add component

BlazorFiddle was updated from Blazor 0.7 to .NET 6.0. Your old source code could not work. You need to upgrade to latest.