Setting figure_format to sag causes UI to break

I have following reproducible code, which causes notebook ui to break, when I set figure_format to svg. Commenting this line fixes the problem.

notebook 6.0.0

```
%config InlineBackend.figure_format = 'svg'
%matplotlib inline
import matplotlib.pyplot as plt

plt.plot(range(10), '-o')
```

Reproducible on latest Safari, Chrome and Firefox.

Start by running the provided notebook snippet with InlineBackend.figure_format set to 'svg' in notebook 6.0.0 across Safari, Chrome, and Firefox, then compare it with the raster-format case. Done means the notebook UI remains usable and the plotted figure renders correctly when SVG output is enabled.

Written by the indexing model from the issue text.