In The Sims 4, using the default underwear with leggings gives Sims a panty line. If you use the lace-trimmed underwear pictured on the bottom, it eliminates the panty line. : r/GamingDetails
Leggings CC & Mods for The Sims 4 — SNOOTYSIMS
10 Fleece-Lined Leggings — Best Fleece-Lined Leggings for Winter
Legging at The Sims 4 Nexus - Mods and community
Medium Legging at The Sims 4 Nexus - Mods and community