Installed webpack encore and configured js and css to use it.

config/bundles.php

@@ -12,4 +12,5 @@ return [
     Symfony\Bundle\MonologBundle\MonologBundle::class => ['all' => true],
     Symfony\Bundle\MakerBundle\MakerBundle::class => ['dev' => true],
     Sensio\Bundle\FrameworkExtraBundle\SensioFrameworkExtraBundle::class => ['all' => true],
+    Symfony\WebpackEncoreBundle\WebpackEncoreBundle::class => ['all' => true],
 ];