Desktop,Mobile: Fixes #10785: Fix math is invisible in certain mermaid diagrams

[personalizedrefrigerator]

Summary

The upgrade Mermaid to v10.9.1 included support for math expressions in mermaid diagrams.

Joplin renders Mermaid diagrams within <pre>s which have white-space: pre by default. This breaks math expressions in certain diagrams. A previous commit partially fixed this for sequence diagrams (see comment). However, the change doesn't seem sufficient to fix the issue for all sequence diagrams (or perhaps even most? See #10785.).

Resetting the white-space to unset directly on the <pre>, rather than on its direct <svg> descendants seems to fix the issue for the sequence diagram provided in #10785.

Fixes #10785.

Screenshot

Testing plan

1. Create a new note.
2. Copy the Mermaid code block for the sequence diagram provided in bug of rendering a mermaid graph #10785 (using markdown GitHub's "quote reply" option).
3. Verify that math expressions are visible in the rendered note.

This has been tested successfully on Ubuntu 24.04.

[idealkindom]

Summary

The upgrade Mermaid to v10.9.1 included support for math expressions in mermaid diagrams.

Joplin renders Mermaid diagrams within \<pre\>s which have white-space: pre by default. This breaks math expressions in certain diagrams. A previous commit partially fixed this for sequence diagrams (see comment). However, the change doesn't seem sufficient to fix the issue for all sequence diagrams (or perhaps even most? See #10785.).

Resetting the white-space to unset directly on the \<pre\>, rather than on its direct <svg> descendants seems to fix the issue for the sequence diagram provided in #10785.

Fixes #10785.

Screenshot

Testing plan

1. Create a new note.

2. Copy the Mermaid code block for the sequence diagram provided in [bug of rendering a mermaid graph #10785](https://github.com/laurent22/joplin/issues/10785) (using markdown GitHub's "quote reply" option).

3. Verify that math expressions are visible in the rendered note.

This has been tested successfully on Ubuntu 24.04.

Hey. I tried the latest Joplin 3.1.4, it looks that this problem still persist in ver 3.1.4. The string of overall style setting works some how. However when I switch the editor mode I found the bug is still there. And when I try to download the graph in svg, some greek letters were lost. However, if I store the graph in png, it works well.