Typically, citrus yuri manga showcases deep romantic feelings, personal growth of the characters, and sometimes explores societal taboos. The illustrations are usually very appealing.
Some yuri manga similar to Citrus include 'Kase-san and Morning Glories' and 'Aoi Hana'. They have similar emotional depth and relationship developments. Also, 'Whispered Words' might appeal to you if you liked Citrus as it explores similar themes of female friendships and romantic feelings.