The icons are based on those for GNOME terminal in the Adwaita theme.

They were generated by importing the 16x16, 32x32 and 48x48 PNG files
into GIMP as separate layers then exporting as a single .ico file.

The original files are dual-licensed under either the GNU LGPL v3 or
Creative Commons Attribution-Share Alike 3.0 United States License.

The .ico files are licensed under the latter.