A container lid assembly outfits a container includes a lower lid construction and a slider element. The slider element is received in the lower lid construction and is linearly displaceable in a back and forth manner relative to the lower lid construction for opening and closing the container lid. The lower lid construction includes concave surfacing and the slider element includes convex surfacing. The slider element seats atop the lower lid construction such that the convex surfacing and concave surfacing form a spherical surface-to-surface seal and enabling slidable open-close functionality. The slider element is resiliently actuable when seated atop the lower lid construction for enhancing seated engagement therebetween. The slider element includes a step-down formation cooperable with resilient actuation thereof for further enhancing seated engagement between the slider element and the lower lid construction. The container lid further locks to the container when in an actuated lower lid configuration.