positions of regions in drupak8

hi,

i would like to know where the position of the logo, the regions and so are defined.
theres quite a lot information out there about drupal 8 and css, but its all very abstract.

for bartik, i would assume that the information of the logo placement is in
bartik/css/layout.css

but:

/**
 * @file
 * Bartik layout styling.
 */

/**
 * Container
 */
.layout-container {
  max-width: 860px;
  margin-left: auto;
  margin-right: auto;
}
@media all and (min-width: 851px) {
  .layout-container {
    max-width: 1290px;
  }
}

/**
 * Main
 */
.layout-main-wrapper {
  min-height: 300px;
}
.layout-main {
  margin-top: 20px;
  margin-bottom: 40px;
}

looking at that file, theres not much in there.

so where is the logo position?
what is .layout-main-wrapper and the other definitions used for?