### Tasks
- [ ] Improve custom cursors (they are too big + do not support dark mode)
- [ ] Implement dark mode
- [x] Fix bug with toolbar button highlighting
- [ ] Implement dialogs
- [ ] Create custom elements / shadow root (dialogs and main element)
- [ ] Include documentation as self-contained HTML
- [ ] Implement popup menu
- [ ] Center dialogs on editor div
- [ ] Implement drawRectangle
- [ ] Change highlight colour to blue
- [ ] Dialog: OK on the right
- [ ] Copy RXN to clipboard