The sample CSS themes (including scheduler_8) can be found in the zip package (both trial and full versions), in demo/themes directory.
You can also download it directly using this link:
https://javascript.daypilot.org/demo/themes/scheduler_8.css
The theme CSS needs to be added to the page using <link> tag.
<link type="text/css" rel="stylesheet" href="./themes/scheduler_8.css" />
In Angular, you can also add it to styles.css:
@import 'themes/scheduler_8.css';
This way it will be compiled (minified) and merged with the other styles.