1) Base layer: Ibex lightweight merino Woolies long johns OR midweight merino long johns
2) Midlayer: If you are very cold, wear Powerstretch pants (slim fitting or tights) as a midlayer over merino long johns.
3) Outer Layer – Soft Shell Pants: Arcteryx Gamma MX Pants – very wind resistant and lightly insulated with just a very thin soft layer of fleecy material yet highly breathable and stretchy. Favorite winter soft shell pants for colder conditions.
4) Insulated puffy pants that you can get on and off easily at rest stops (and also useful in case of emergency overnight).
Insulated footwear and a gaiter or light overboot like the Forty Below Light Energy TR overboots will also help you stay warm: https://40below.com/products_detail.php?ProductID=13
Have used the above for -5F with windchill to -25-30F up to 15-20F.
Also even though you are day hiking, in winter it's very important to bring the gear and skills you need to make it through an unplanned overnight. A 7 oz emergency SOL bivvy that can get you through the night, albeit not comfortably, is good thing to bring along.