
.x-media-type-icon(@media-type; @add-title; @color; @char) {
  @mt-selector: ~"[data-media-type='@{media-type}']";
  @{mt-selector} > .icon-content::before { color: @color; content: @char; }
  @{mt-selector} > .add-content-title::before { content: "New " @add-title; color: black; }
}

.x-media-type-icon('application/xhtml+xml';              "Content";   #00c; "\f0f6"); /* icon-file-alt */
.x-media-type-icon('application/oebps-package+xml';      "Book";      #c00; "\f02d"); /* icon-book */
.x-media-type-icon('application/vnd.org.cnx.section';    "Section";   #999; ""); /* icon-folder-open */


.x-media-type-icon(@media-type; @add-title; @color; @char) {
  @mt-selector: ~"[data-media-type='@{media-type}']";
  @{mt-selector} > .icon-content::before { color: @color; content: @char; }
  @{mt-selector} > .add-content-title::before { content: "New " @add-title; color: black; }
}

.x-media-type-icon('application/xhtml+xml';              "Content";   #00c; "\f0f6"); /* icon-file-alt */
.x-media-type-icon('application/oebps-package+xml';      "Book";      #c00; "\f02d"); /* icon-book */
.x-media-type-icon('application/vnd.org.cnx.section';    "Chapter";   #999; ""); /* icon-folder-open */

Change "New Section" to "New Chapter"
Change "New Section" to "New Chapter"
