The phrase "to match the belt" means to choose or wear clothes or accessories that have a similar color or style as the belt one is wearing. Full definition
Back in the day, dresses often came with matching belts covered in the same fabric. (blog.colettehq.com)
One of my favorite features was definitely the wide matching belt, which also helped to bring the waistline down to my natural waist (which prefers 16 ″ shoulder to waist). (thedressedaesthetic.com)
Wear your pencil skirt with its own matching belt. (metrostyle.com)