Culottes with flats is all about proportion. Because you are not wearing heels to lengthen, you need to make sure your shirt-to=pant ratio is just right. You can accomplish this by making sure your shirt is either tucked in your culottes, or that your shirt is a cropped length and ends just above the waistband. That will ensure that your proportions are in tact. You’re going to see culottes a lot in the next few months so you may as well accept it now!
Culottes + cropped or tucked in shirt +flats of all sorts (tennis shoes, slip-ons, sandals, etc…) + accessories of all sorts + bewildering, but awesome compliments that you will redoubtably receive