A closure element of the press-twist type for closing a container, comprising: - a capsule having a side wall extending about an axis, and a transverse panel extending transversely to said axis, - a seal for sealingly engaging with a mouth of the container, wherein the seal is made of a PVC-free material and comprises: - a side portion arranged in contact with the side wall of the capsule; - a front portion extending from the side portion towards said axis, the front portion being delimited by a sealing surface intended to contact an edge of the container, said edge delimiting the mouth; - deformability promoting means for increasing deformability of the front portion, the deformability promoting means comprising a recessed zone configured to be at least partially filled by the material forming the front portion when the front portion is pressed against said edge, so that said edge may penetrate into the thickness of the front portion, thereby sealingly closing the container, characterised in that the seal further comprises a plurality of longitudinal ribs projecting from the side portion towards the inside of the closure element, so as to engage with at least one fixing element provided on the container, at least a first group of ribs of said plurality comprising ribs having respective inserting ends, the inserting ends being beveled or rounded for promoting application of the closure element onto the mouth by pressure, wherein the seal is annular, the sealing surface is conformed as a flat annular surface, and the plurality of ribs comprises a second group of ribs which are shaped differently from the ribs of the first group, the ribs of the second group having respective spacer ends each of which is delimited by an abutment surface, the abutment surface being intended to contact a transverse panel of an adjacent closure element for preventing the adjacent closure element from penetrating excessively inside of said closure element. - a capsule having a side wall extending about an axis, and a transverse panel extending transversely to said axis, - a seal for sealingly engaging with a mouth of the container, - a side portion arranged in contact with the side wall of the capsule; - a front portion extending from the side portion towards said axis, the front portion being delimited by a sealing surface intended to contact an edge of the container, said edge delimiting the mouth; - deformability promoting means for increasing deformability of the front portion, the deformability promoting means comprising a recessed zone configured to be at least partially filled by the material forming the front portion when the front portion is pressed against said edge, so that said edge may penetrate into the thickness of the front portion, thereby sealingly closing the container, characterised in that the seal further comprises a plurality of longitudinal ribs projecting from the side portion towards the inside of the closure element, so as to engage with at least one fixing element provided on the container, at least a first group of ribs of said plurality comprising ribs having respective inserting ends, the inserting ends being beveled or rounded for promoting application of the closure element onto the mouth by pressure, wherein the seal is annular, the sealing surface is conformed as a flat annular surface, and the plurality of ribs comprises a second group of ribs which are shaped differently from the ribs of the first group, the ribs of the second group having respective spacer ends each of which is delimited by an abutment surface, the abutment surface being intended to contact a transverse panel of an adjacent closure element for preventing the adjacent closure element from penetrating excessively inside of said closure element.