Two steps are required:
1. Include the theme in the global CSS (styles.css):
@import url('themes/your_theme.css');
2. Activate it using the "theme" config property:
config: DayPilot.SchedulerConfig = {
theme: "your_theme",
// ...
}
See also the following tutorial:
https://code.daypilot.org/81784/angular-scheduler-css-themes