gitlabhq/app/assets/stylesheets/sections/editor.scss

.file-editor {
  #editor{
    height: 500px;
    width: 100%;
    position: relative;
  }
  .editor-commit-comment {
    padding-top:20px;
    textarea {
      width: 50%;
      margin-left: 20px;
    }
  }
}