Standard markdown links are more or less first class citizens now in Obsidian. See this, even for links with spaces.
However, standard markdown links have the same DOM representation as external links, which makes them indistinguishable from external links in CSS. These links have neither internal-link nor cm-hmd-internal-link classes.
This is something some themes rely on, to say, make internal links purple but external links blue as they would be on the web. Standard markdown links to internal content can only look like external links with this issue.
In the live preview DOM, external links and these outlier internal links look like this:
<span class="cm-link">
<span class="cm-underline">
link title
</span>
</span>
While normal internal links look like this:
<span class="cm-hmd-internal-link">
<span class="cm-underline">
link title
</span>
</span>
I originally posted this here.