David Gervais has kindly agreed to share large format versions of the backgrounds used for several of the UI elements, so that others can easily create their own and keep the same style.
Download:
SE5 Icon Backgrounds
The included files are for:
Bmp_TechIcons, Bmp_CulturalAchievements, Bmp_IntelligenceAchievements
Buttons_Combat_Orders
Bmp_DamageTypes (same as combat orders, but cropped)
Buttons_GroundCombat_Orders
Buttons_Orders