Source (required if based on other people's work): https://github.com/alxlg/breeze-la-capitaine-icons
La Capitaine theme has awesome icons for application launchers but in KDE Plasma is not very complete and integrated like the default Breeze. This icon theme depends in fact on Breeze (you need it installed!) but adds La Capitaine icons for applications on top of it. Credits to Breeze and La Capitaine contributors.