The phrase "nice complement" means something that goes well with or adds to something else. It is like when two things or people complement each other nicely, making each other better or more complete. Full definition
Even if you have done a post kind of like this one before, I think this is a really nice complement to yesterday's post. (looplooks.net)
Those shorts are fashionable but look so comfy too and I love the background for your shoot - great contrast but also nice complement to the clothes (color-wise)! (seekingsunshine.com)
Nitro: Youth Energy, The Meaning of Life, and Staring at the Sun are all nice complements to All I Want. (gameological.com)