Yii2 在view里加css

$this->registerCssFile("http://example.com/css/themes/black-and-white.css",
 [BootstrapAsset::className()], ['media'=>'print'],'css-print-theme');

还可以设置其它项：
$this->registerLinkTag([
    'title'=>'Lives
 News for Yii Framework',
    'rel'=>'alternate',
    'type'=>'application/rss+xml',
    'href'=>'http://www.yiiframework.com/rss.xml/',
]);


$this->registerMetaTag(['encoding'=>'utf-8']);
$this->registerJsFile('http://example.com/js/main.js',
 [JqueryAsset::className()]);