1. The code implementation in the view is as follows  ?>)
When the URL is http://official.local/case, the generated 
results in an image URL of http://official.local/static/images/header/top.png, returning a 200 response.
When the URL is http://official.local/case/, the generated 
results in an image URL of http://official.local/case/images/top.png, returning a 404 response. How can this be resolved? See Figure 1.
2. Viewing the page source code of http://official.local/case/, the generated results in an image URL of http://official.local/case/images/top.png, returning a 404 response. See Figure 2.
3. Checking the Debug information, an error had already occurred, returning a 404 response: yii\base\InvalidRouteException: Unable to resolve the request “case/”. See Figure 3.
yii\base\InvalidRouteException: Unable to resolve the request "case/". in C:\wwwroot\official-website-management-system\src\vendor\yiisoft\yii2\base\Module.php:561
Stack trace:
#0 C:\wwwroot\official-website-management-system\src\vendor\yiisoft\yii2\web\Application.php(103): yii\base\Module->runAction('case/', Array)
#1 C:\wwwroot\official-website-management-system\src\vendor\yiisoft\yii2\base\Application.php(384): yii\web\Application->handleRequest(Object(yii\web\Request))
#2 C:\wwwroot\official-website-management-system\src\frontend\web\index.php(18): yii\base\Application->run()
#3 {main}
Next yii\web\NotFoundHttpException: Page not found. in C:\wwwroot\official-website-management-system\src\vendor\yiisoft\yii2\web\Application.php:115
Stack trace:
#0 C:\wwwroot\official-website-management-system\src\vendor\yiisoft\yii2\base\Application.php(384): yii\web\Application->handleRequest(Object(yii\web\Request))
#1 C:\wwwroot\official-website-management-system\src\frontend\web\index.php(18): yii\base\Application->run()
#2 {main}
4. Ultimately, I implemented a small helper class method.
public static function url($path): string
{
$cdn = Yii::$app->params['cdnDomainHttps'] ?? '';
return rtrim($cdn, '/') . '/' . ltrim($path, '/');
}