What electrical wires are ok for 90C flushmount lighs?
NM-B is rated for 90°C.  Here's an excerpt from Southwire’s Romex® SIMpull® Type NM-B web page.

Southwire’s Romex® SIMpull® Type NM-B (non-metallic sheathed cable) may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90°C...

From NEC

National Electrical Code 2017
Chapter 3 Wiring Methods and Materials
Article 334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS
334.112 Insulation. ...Conductor insulation shall be rated at 90°C (194°F).

However, keep in mind that the ampacity is limited to that of a 60°C conductor.