Check the documentation of angular CLI on how to install global libraraies,
you have to modify your angular-cli.json file to include css files in bundled style file not use directly in the HTML.
"styles": [
"../node_modules/ng2-toastr/bundles/ng2-toastr.min.css"
]
If for some reason you dont want to include them in bundled style file, you may add it in assets array in cli json file, and can add a link in the HTML file
"assets": [
"../node_modules/ng2-toastr/bundles/ng2-toastr.min.css"
]
Hope this helps!!