Answer by taking a quote from the following article:

Stereolab were an English-French avant-pop band from London, formed in 1990 by Tim Gane (guitar/keyboards) and Laetitia Sadier (vocals/keyboards/guitar) who both remained at the songwriting helm across many line-up changes. Other long-time members included Mary Hansen (backing vocals/keyboards/guitar), who joined in 1992 and remained in the line-up until her accidental death in 2002, and Andy Ramsay (drums), who joined in 1993 and is still in the official line-up. Sean O'Hagan of the High Llamas was a member from 1993 to 1994, and continued appearing on later records for occasional guest appearances. The group's music combined influences from krautrock, lounge and 1960s pop music.

Stereolab's music combines a droning rock sound with lounge instrumentals, overlaid with sing-song female vocals and pop melodies. It has been generally described as avant-pop, indie pop, art pop, indie electronic, indie rock, post-rock experimental rock, and experimental pop. Their records are heavily influenced by the "motorik" technique of 1970s krautrock groups such as Neu! and Faust. Tim Gane has supported the comparison: "Neu! did minimalism and drones, but in a very pop way." Funk, jazz, and Brazilian music were additional inspirations, and the sounds influenced by minimalist composers Philip Glass and Steve Reich can be found on the 1999 album Cobra and Phases Group Play Voltage in the Milky Night. Regarding their later work such as Instant 0 in the Universe (2003) and Margerine Eclipse (2004), critics have compared the releases to their earlier guitar-driven style. Stereolab's style also incorporates easy-listening music of the 1950s and '60s. Joshua Klein in The Washington Post said that, "Years before everyone else caught on, Stereolab was referencing the 1970s German bands Can and Neu!, the Mexican lounge music master Esquivel and the decidedly unhip Burt Bacharach."  Stereolab make use of vintage electronic keyboards and synthesizers from brands such as Farfisa and Vox and Moog. Gane has praised the instruments for their versatility: "We use the older effects because they're more direct, more extreme, and they're more like plasticine: you can shape them into loads of things." The 1994 album Mars Audiac Quintet prominently feature Moog synthesizers.  Laetitia Sadier's English and French vocals was a part of Stereolab's music since the beginning; and would occasionally sing wordlessly along with the music. In reference to her laid-back delivery, Peter Shapiro wrote facetiously in The Wire that she "display[ed] all the emotional histrionics of Nico". Sadier would often trade vocals with Mary Hansen back-and-forth in a sing-song manner that has been described as "eerie" and "hypnotic". After Hansen's death in 2002, critic Jim Harrington commented that her absence is noticeable on live performances of Stereolab's older tracks, and that their newer songs could have benefited from Hansen's backing vocals.  In interviews, Gane and Sadier have discussed their musical philosophy. Gane said that "to be unique was more important than to be good." On the subject of being too obscure, he said in a 1996 interview that "maybe the area where we're on dodgy ground, is this idea that you need great knowledge [of] esoteric music to understand what we're doing." Sadier responded to Gane, saying that she "think[s] we have achieved a music that will make sense to a lot of people whether they know about Steve Reich or not." The duo were up-front about their desire to grow their sound: for Gane, "otherwise it just sounds like what other people are doing", and for Sadier, "you trust that there is more and that it can be done more interesting."

How has Stereolab's style been described?
Stereolab's music combines a droning rock sound with lounge instrumentals, overlaid with sing-song female vocals and pop melodies.