You can submit your own themes as a pull request to make them available to all users.
To create a theme simply create a my-theme.theme.scss
file under src/themes/
and add a global class selector named after your theme.
/* src/themes/my-theme.theme.scss */
.my-theme {
// Your styles here
}
Enable your theme in your configuration to see your changes:
theme: my-theme
Themes use CSS Custom Properties for variables.
There are quite a few variables out there to make theme development easier. Take a look at existing themes for a list of variables or check out your browser's dev tools.