I use my magic mirror in landscape format. And I two place four modules side by side. My idea was to divide the top_center position in two.

Therefore I added new region definitions in the custom.css:

.region.top.center1 {
  left: 33%;
  -moz-transform: translateX(-33%);
  -o-transform: translateX(-33%);
  -webkit-transform: translateX(-33%);
  -ms-transform: translateX(-33%);
  transform: translateX(-33%);
}

.region.top.center2 {
  left: 60%;
  -moz-transform: translateX(-33%);
  -o-transform: translateX(-33%);
  -webkit-transform: translateX(-33%);
  -ms-transform: translateX(-33%);
  transform: translateX(-33%);
}

.region.top.center1,
.region.top.center2 {
  top: 100%;
}

And use in the config.js

module: 'MMM-Fuel',
position: 'top_center1', 
config: {

Of course, this doesn’t work. I read something, about a region class definition. But I didn’t found, what else I have to do. Any ideas what is missing?