An accessory that comprises: - a façade plate that comprises a frame that is defined between an outer peripheral edge and an inner peripheral edge (121c,122c, 123c) that defines an opening; - an accessory support that is mounted to tilt through said opening between a lowered position in which it extends below the façade plate, and a raised position in which a major portion thereof extends above the façade plate; - a locking system that comprises firstly at least one locking arm that extends longitudinally between one end portion forming a blocking portion and another opposite end portion forming an actuator portion and that is movable between a locking position in which said blocking portion bears against a blocking surface of the accessory support and a release position in which said blocking portion is spaced apart from said blocking surface, and secondly an actuator button, distinct from the accessory support, which firstly comprises a presser wall placed above a branch of the frame delimited between a portion of said outer and inner peripheral edges and having a front face which forms a bearing surface for a user's finger, and secondly, cooperates with said locking arm so as to control the movement of this locking arm, this actuator button being tiltable about a tilt axis which extends parallel to the mean plane of said façade plate, between a standby position in which said front face of said presser wall extends substantially parallel to the mean plane of the façade plate and an actuated position, tilted towards the outside of the façade plate,in which said presser wall moves closer to the outer peripheral edge of said façade plate with its front face sloping relative to the mean plane of the façade plate, wherein said locking arm is pivotable about a pivot axis situated close to its actuator portion and perpendicular to said tilt axis of the actuator button, wherein the actuator button includes an actuator rib of height that extends rearwards from the rear face of the presser wall, substantially perpendicularly to said presser wall, said actuator rib being in permanent contact with said actuator portion of said locking arm, and wherein resilient return means are provided that are compressed between said locking arm and said actuator rib in order to continuously push said locking arm into its locking position and also continuously act on said actuator button in order to return it to its standby position. - a façade plate that comprises a frame that is defined between an outer peripheral edge and an inner peripheral edge (121c,122c, 123c) that defines an opening; - an accessory support that is mounted to tilt through said opening between a lowered position in which it extends below the façade plate, and a raised position in which a major portion thereof extends above the façade plate; - a locking system that comprises firstly at least one locking arm that extends longitudinally between one end portion forming a blocking portion and another opposite end portion forming an actuator portion and that is movable between a locking position in which said blocking portion bears against a blocking surface of the accessory support and a release position in which said blocking portion is spaced apart from said blocking surface, and secondly an actuator button, distinct from the accessory support, which firstly comprises a presser wall placed above a branch of the frame delimited between a portion of said outer and inner peripheral edges and having a front face which forms a bearing surface for a user's finger, and secondly, cooperates with said locking arm so as to control the movement of this locking arm, this actuator button being tiltable about a tilt axis which extends parallel to the mean plane of said façade plate, between a standby position in which said front face of said presser wall extends substantially parallel to the mean plane of the façade plate and an actuated position, tilted towards the outside of the façade plate,in which said presser wall moves closer to the outer peripheral edge of said façade plate with its front face sloping relative to the mean plane of the façade plate, wherein said locking arm is pivotable about a pivot axis situated close to its actuator portion and perpendicular to said tilt axis of the actuator button, wherein the actuator button includes an actuator rib of height that extends rearwards from the rear face of the presser wall, substantially perpendicularly to said presser wall, said actuator rib being in permanent contact with said actuator portion of said locking arm, and wherein resilient return means are provided that are compressed between said locking arm and said actuator rib in order to continuously push said locking arm into its locking position and also continuously act on said actuator button in order to return it to its standby position.