One way is using : URL::asset('css/file.css');
For using {{ HTML::style('css/style.css') }}, you will have to go through following steps:
Add the following lines in the require section of composer.json file and run composer update "illuminate/html": "5.*".
Register the service provider in config/app.php by adding the following value into the providers array:
'Illuminate\Html\HtmlServiceProvider'
Register facades by adding these two lines in the aliases array:
'Form'=> 'Illuminate\Html\FormFacade',
'HTML'=> 'Illuminate\Html\HtmlFacade'