doc: adapt more to m.css changes.

I'm blind.

Doxyfile-mcss

@@ -100,7 +100,7 @@ ALIASES                = \
 
 HTML_EXTRA_STYLESHEET = \
     https://fonts.googleapis.com/css?family=Source+Sans+Pro:400,400i,600,600i%7CSource+Code+Pro:400,400i,600&subset=latin-ext \
-    ../css/m-dark+doxygen.compiled.css
+    ../css/m-dark+documentation.compiled.css
 
 ##! M_PAGE_FINE_PRINT = "<p>Magnum docs. Part of the <a href="https://magnum.graphics/">Magnum project</a>, copyright © <a href="http://mosra.cz/">Vladimír Vondruš</a> and contributors, 2010&ndash;2019.<br />Generated by <a href="https://doxygen.org/">Doxygen</a> {doxygen_version} and <a href="https://mcss.mosra.cz/">m.css</a>. Contact the team via <a href="https://github.com/mosra/magnum">GitHub</a>, <a href="https://gitter.im/mosra/magnum">Gitter</a>, <a href="mailto:info@magnum.graphics">e-mail</a> or <a href="https://twitter.com/czmosra">Twitter</a>.</p>"