Message Grouping header font

It's possible to change the font and/or background color used for the Message Grouping headers (such as "Today", "Yesterday", and "Last Week") in the message-list pane. To do so, exit Thunderbird and insert the following code into your userChrome.css file, adjusting for your own font and color preferences as desired.

For the font, use the following code:

/*Grouped by Sort headers: font */
treechildren::-moz-tree-cell-text(dummy){
  font-size: 12pt !important;
  font-family : Arial !important;
  color:blue !important;
}

For the background color of the entire header row, include the following code:

/*Grouped by Sort headers: background */
treechildren::-moz-tree-row(dummy){
  background: silver !important;
}

If you want the selected header row to be a different color, also include:

/*Grouped by Sort headers: background for selected header */
treechildren::-moz-tree-row(dummy, selected, focus){
  background: yellow !important;
}

Instead of specifying color values with words ("blue", "silver", etc.), you can use hex values (e.g., "#FFC0CB" for pink). This color blender is convenient.