Features

• Consistently support Widget.description tooltips by @philippjfr in #393
• Add SplitButton widget by @dalthviz in #284
• Add MenuToggle by @ahuang11 in #406

Enhancements

• Add ChatInterface.input_params by @ahuang11 in #401
• Optimize font CSS lookups by @philippjfr in #399
• Allow rendering components into Accordion and Tabs headers by @philippjfr in #409

Design Tweaks

• Reduce default Typography header size by @philippjfr in #394, #404, #410
• Align IconButton and ToggleIcon sizing by @philippjfr in #411
• Change ChatMessage placeholder loading animation by @philippjfr in #417

Bug Fixes

• Only jslink on Widget instances, not WidgetBase by @maximlt in #390
• Allow setting open on MenuList items by @philippjfr in #395
• Fix regression adding items to MenuList by @philippjfr in #396
• Ensure classic panel components are styled correctly by @philippjfr in #408
• Handle sync of MuiNotification model by @philippjfr in #412
• Fix handling of decimal values in NumberInput validation by @philippjfr in #413
• Ensure material-variables CSS does not override font and color by @philippjfr in #419

Documentation

• Review SplitButton Reference Guide by @MarcSkovMadsen in #398
• Add missing notebooks by @MarcSkovMadsen in #368

New Contributors

• @dalthviz made their first contribution in #284

Full Changelog: v0.3.3...v0.4.0