CSS Flexbox is not supported at all on IE9 so we use lt-10 to indicate lower then 10 version of IE. The class is used by our threedots implementation to revert back to the previous way of threedotting stuff (meaning with fixed widths). Having flexbox greatly improves how threedotting works as it doesn't require widths to be set anymore and allows the truncated fields to take as much space as they can get unless otherwise specified. Once we drop support for IE9 we can drop all CSS selectors that are prefixed with the .lt-10 class. Removing this fallback will be trivial.