mermaid: choosing <div> over <p> for styling flexibility

[nnzv]

Enhance styling and centering by opting for <div> over <p>. For example, utilize the class div.mermaid with text-align: center; for positioning the Mermaid.js SVG image at the center of the container.

// filepath: assets/_custom.scss
div.mermaid {
    text-align: center;
}

[alex-shpak]

Hello!
<p> is used to apply regular spacing (as many other blocks in markdown are rendered as paragraphs). How this will be different from p.mermaid {} class?

[alex-shpak]

In the end another PR was merged changing p to pre.
#613