Maybe it’s a reaction to the bombastic, synth-heavy Europop that’s been saturating American top 40 radio, but piano ballads are all the rage now — from Bruno Mars’ soul-bearing “When I Was Your Man” to Lana Del Rey’s string-swathed “Young & Beautiful” to Rihanna’s vulnerable “Stay.” Next on the list is British singer/songwriter Timothy McKenzie, better-known as Labrinth, who is snaking his way stateside with “Beneath Your Beautiful,” a seductive ode to inner beauty. “Beautiful,” from Labrinth’s debut album “Electronic Earth,” is already a ubiquitous smash in the United Kingdom. But no matter what continent you’re on, it’s an enduring heart-melter. Over a backdrop of piano, hip-hop drums and synth-bass, McKenzie trades verses with Scottish crooner Emile Sande: “You’ve built your wall so high that no one could climb it,” he pleads, “but I’m gonna try.” With the song now charting in the United States, Labrinth is hoping to make another nation swoon.