Complex sentence: Although the ice giants also have hydrogen envelopes, these are much smaller, accounting for only about 10% or less of their mass. Their hydrogen also never reaches the depths necessary for the pressure to create metallic hydrogen.
Split into simpler sentences: Although the ice giants also have hydrogen envelopes, these are much smaller. They account for less than 20% of their mass. Their hydrogen also never reaches the depths necessary for the pressure to create metallic hydrogen.