The lines in bold below are missing from resources/sass/app.scss in ST2.1.0 Final
You'll need them in order to rebuild your style sheets.

@include sencha-panel;
@include sencha-buttons;
@include sencha-sheet;
@include sencha-picker;
@include sencha-tabs;
@include sencha-toolbar;
@include sencha-toolbar-forms;
@include sencha-indexbar;
@include sencha-list;
@include sencha-layout;
@include sencha-carousel;
@include sencha-form;
@include sencha-msgbox;
@include sencha-loading-spinner;
@include sencha-draw;
@include sencha-charts;

Feedback to Sencha Dev Team:

You might also consider adding these to config.rb so devs can exactly reproduce the exact same app.css that ships with the product and (better) ensure that your build process for these generate files follows exactly what end user devs will do. This would have avoided this bug.

environment = :development
output_style = :expanded

# output_style = :compressed
# environment = :production

Currently, by default it generates compressed production CSS files. When you do switch to performing a development/expanded CSS the relative source code paths in the resulting app.css are different so spotting changes using a diff tool is more painful.