<blockquote>
<p>Apologies for the delay in responding - the last few weeks have been super busy.</p>
</blockquote>
<p>Never mind - we are all volunteers.</p>
<blockquote>
<p>What operating system / distribution are you running? That could have an effect on the TreeView line colors. If possible, I think it would be better to use a color from the underlying GTK theme rather than hard-coding black.</p>
</blockquote>
<p>I am using Ubuntu 18.04.2 and a gnome desktop. I lately implemented the option to show tree lines for the workbench plugin's sidebar and there I also see red lines. So most likely you are right - it seems to be a local problem not a general one. I will remove the CSS part which sets the border color.</p>

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