Presenter cursor lacks contrast on dark backgrounds (images)

[franky47]

Describe the bug
A clear and concise description of what the bug is.

The presenter cursor can lack contrast against dark backgrounds in light mode, and light backgrounds in dark mode.

To Reproduce
Steps to reproduce the behavior:

1. Open Slidev in demo mode (pnpm demo:dev), and toggle the theme
2. Observe the cursor against different backgrounds

Here's an example, where in dark mode (white cursor), the contrast is acceptable:

But switching to light mode turns the cursor completely black, which lacks contrast against the same background:

Another demo of the issue which happened live while presenting (though the light/dark theme was a saver for bad projector contrast, kudos for that!):
https://youtu.be/PEWtI5PwQ30&t=58

Desktop (please complete the following information):

• OS: macOS 12.7.3
• Browser: Firefox 124
• Slidev version: 0.48.7 (built from source from the main branch at time of opening the issue)

Suggestion

I fixed it locally by adding a contrasting stroke on the cursor icon:

I'll open a PR with this fix.