You can use collection from Phalcon
$this->assets ->collection('styles')
->addCss('assets/css/bootstrap.min.css')
->AddCss('assets/css/general.css');
and in view
<head>
<meta charset="utf-8">
{{ assets.outputCss('styles') }}
</head>
and you can add any css (or js) in any actions
function someAction() {
$this-assets->collection('styles')->addCss('assets/css/some.css');
}
By the way, all of this you can find in documentaion.