Question about the pokestop badge

The blue line means you haven't spun it since the update, you then get 250 XP for it, but that's a one-time bonus.

Thats the EXP bar for the badge.

Based on my gameplay:
Once the badge reaches bronze you get 1 bonus item from spinning the gym stop. Silver get 2 bonus items from spinning the stop.

You level up the badge by:
Feeding berries to pokemon in the gym,
Clearing the gym from rivals.
Placing your defender into the gym.