<p>I'm not familiar with this theme, or even GTK+2 theming in general, but from a quick search, it looks like this theme requires Nodoka theme engine, which presumably has to be installed separately.</p>
<p>Two suggestions:</p>
<ul>
<li>Test with another GTK+2 application and see if it works. If it doesn't then it's probably unrelated to Geany and should be raised with GTK+ or the theme engine authors. I know the open source application <a href="https://hexchat.github.io/" rel="nofollow">Hexchat</a> works on Windows and uses GTK+2, if you can't think of any other GTK+2 windows apps.</li>
<li>Try some other themes, particularly any which might be shipped by default, and see if they work. If so, it's probably something related to Nodoka like not having it installed.</li>
</ul>
<p>Most likely there will be some debug messages printed if/when the theme fails to load, which you can see using <code>Help->Debug Messages</code>.</p>

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