Portable electronic devices are provided. A device may include cover glass with a light mask. The light mask may be microperforated to allow light to pass through the light mask. The microperforations may allow light to pass through the light mask. The devices may include sensors and light emitters that receive and transmit light through the microperforations. The devices may include a variable cantilever spring as part of a button assembly. The spring may be flattened against itself without exceeding its elastic limit. The devices may include display modules. The display module may include structures that block light from leaking out of the module. The structures may include opaque tapes, opaque enclosures for the display module, and other suitable structures.