Install claws-mail-themes by entering the following commands in the terminal:
sudo apt update sudo apt install claws-mail-themes
Description:
Pixmap icon themes for the Claws Mail mailer
These are the user contributed icon themes for the Claws Mail mailer. Currently includes 39 icon themes from various authors: . achileus-noname A_Ducks_Claw black Blaue_Klaue blue_anarchy clawsola Coons-Blue-0.3 Crystal elementary Everaldo_Kids Fugue Gnomaws-0.6a Gnome gnome-brave Gnomeria Gorillaws Graphitte-0.9.7 hydroxygen Korillaws Kovico-claws Logos-1.0.1 mongrel mongrel2 mozilla Navigator New_Session Old_Dark_Theme orbit-claws Phoenity Plain_and_Bluish Skypilot_Clawssic stw Sylpholution SylZilla Tango_v1.2.1 tml02c tom_2.1.1 UltimateClawsMail0.5.1 XeNtish
Homepage: http://www.claws-mail.org/themes.php
Version: 20140629+dfsg1-1
Section: universe/mail