Inline styles are not compatible with CSP

[rassie]

Describe the bug
With CSP (Content Security Policy) enabled, inline styles are blocked, which leads to progress bars not working. Incompatibility with CSP is bad in general and worse in environments like Electron, which strongly recommend enabling CSP. While it's possible to enable unsafe-inline as a workaround, this is strongly discouraged.

To Reproduce

1. Add CSP headers to a project with awesome-notifications
2. Observe warnings and errors in the browser console

Expected behavior
No CSP errors or warnings should be displayed.

Additional context
This problem can apparently be solved by changing styles dynamically instead of generating those inside an HTML element. See https://stackoverflow.com/a/57633457/6460 for details and an example.