I recently received a copy of Magento 2 Theme Design book by Fernando J Miguel.

The book is designed to be a guide for web designers and developers wanting to get started with building Magento 2 themes. As author of Magento theming books for Magento 1 (mostly recently, Magento Responsive Theme Design), I’m credited on the cover, and I acted as technical reviewer on the book.
Table of contents
- INTRODUCTION TO MAGENTO 2
- EXPLORING MAGENTO THEMES
- MAGENTO 2 THEME LAYOUT
- MAGENTO UI LIBRARY
- CREATING A RESPONSIVE MAGENTO 2 THEME
- MAGENTO 2 STYLES DEBUGGING
- MAGENTO UI COMPONENTS
- MAGENTO LAYOUT DEVELOPMENT
- MAGENTO 2 JAVASCRIPT
- SOCIAL MEDIA IN MAGENTO 2
- THEME DEVELOPMENT BEST PRACTICES
- MAGENTO THEME DISTRIBUTION