There are 3 repositories under kodi-skin topic.
Modification of Kodi's default skin for lower resolutions.
A HTML, CSS, and JavaScript framework that looks like the default Kodi theme.
Auramod Skin for Kodi 19+
✨ Kodi frontend skin optimized for low-power devices like the Raspberry Pi, originally based on reFocus Big. Thread can be found on the official Kodi.tv forum:
Confluence-MOD for KODI V18 Leia
Kodi.tv (Nexus) skin - This is mostly an update of Estuary skin.