ui/app/styles/vendor

Vendors

Most projects will have a vendors/ folder containing all the CSS files from external libraries and frameworks – Normalize, Bootstrap, jQueryUI, FancyCarouselSliderjQueryPowered, and so on. Putting those aside in the same folder is a good way to say “Hey, this is not from me, not my code, not my responsibility”.

If you have to override a section of any vendor, I recommend you have an 8th folder called vendors-extensions/ in which you may have files named exactly after the vendors they overwrite. For instance, vendors-extensions/_bootstrap.scss is a file containing all CSS rules intended to re-declare some of Bootstrap’s default CSS. This is to avoid editing the vendor files themselves, which is generally not a good idea.

Reference: Sass Guidelines > Architecture > Vendors folder