CSS issues with Jupyter Notebook 7.3

[jtpio]

Description

When opening the slideshow with Jupyter Notebook 7.3.2:

Reproduce

Open a notebook with Jupyter Notebook 7.3, then open in slideshow mode.

Expected behavior

Context

• jupyterlab-slideshow==0.3.0
• notebook==7.3.2

[brichet]

Thanks @jtpio for opening this.
Indeed there are some CSS rules added in Notebook application, we need to overwrite it.

[brichet]

Fixed by #23