Using Theme 3.0.2 and NativeScript 8.1

[dlcole]

I'm about to migrate a large JavaScript project from NativeScript 6.8 to to 8.1. As part of this effort I want to revise the UI to take full advantage of Theme 3.0.2. I've read what documentation I can find (ReadMe's and blogs), but some basic questions remain. For example, if I create a new tabbed project, the app-root.xml file looks like this:

<TabView androidTabsPosition="bottom">
    <TabViewItem title="Home" >
        <Frame defaultPage="home/home-items-page" />
    </TabViewItem>

    <TabViewItem title="Browse" >
        <Frame defaultPage="browse/browse-page" />
    </TabViewItem>

    <TabViewItem title="Search" >
        <Frame defaultPage="search/search-page" />
    </TabViewItem>
</TabView>  

Note that there are no classes or styles specified. The _app-common.scss file includes:

// Custom tabstrip item class
.navigation__item {
  &:active,
  &:active Label {
    @include colorize($contrasted-color: complementary background 20% 0%);
  }
}

I understand that Theme specifies styles based on the element name, so how would I know that the .navigation__item class controls the formatting of the tabs? I can't even find the class when I search the Theme source code. Similarly, while I can see some examples of using the colorize mixin, I can't find a description of what the parameters are or what they mean.

Theme looks very powerful and I'd really like to use it as intended. Is there any guidance for using Theme in a current NativeScript project beyond the ReadMe? Based on this SO post, I'm not alone with my question.