It looks like the \n
bits are just line breaks inserted for visibility.
So, this is a single css style declaration:
.tc-board-column-action {visibility: hidden;}
If so, it can be anywhere the body of a tiddler tagged `$:/tags/Stylesheet
I suspect, however, that this is not the css that will prevent drag&drop.
I don’t know kanban, but I did quickly checking by adding a simple stylesheet with that specification to
https://ibnishak.github.io/Tesseract/projects/tekan/Tekan.html
and it did not prevent drag and drop.
You can search for “dropzone” in shadow tiddlers in the advanced search tab
The core has its dropzone specified like this in the page template:
<$dropzone>
<$list filter="[all[shadows+tiddlers]tag[$:/tags/PageTemplate]!has[draft.of]]" variable="listItem">
<$transclude tiddler=<<listItem>>/>
</$list>
</$dropzone>
It’s not ideal to mess with core shadow templates. But you should see that if you remove both dropzone tags (starting and ending) — but NOT the stuff sandwiched between! — the dropzone is no longer active but the page displays normally.
If you do modify the shadow: I highly recommend adding some kind of inline comment where you modify a shadow tiddler. (I also add a “notes” field, so that before upgrading, I can easily check which shadows have been modified, and for what reason, so that I can reconstruct my changes when there’s an upgrade to TiddlyWiki core.)
<!-- <$dropzone></$dropzone> tags removed from around the following list of page template tiddlers -->
<$list filter="[all[shadows+tiddlers]tag[$:/tags/PageTemplate]!has[draft.of]]" variable="listItem">
<$transclude tiddler=<<listItem>>/>
</$list>
There may be some other dropzone tiddlers specifically included with Tekan. If so, a similar treatment should suffice.