Non-image file icons are inverted on hover

boards/models/attachment/viewers.py

@@ -67,7 +67,7 b' class AbstractViewer:'
             image = FILE_STUB_IMAGE
 
         return '<a href="{}">'\
-               '<img src="{}" width="200" height="150"/>'\
+               '<img class="url-image" src="{}" width="200" height="150"/>'\
                '</a>'.format(self.file.url, static(image))
 
 
@@ -145,5 +145,5 b' class UrlViewer(AbstractViewer):'
                '</div>'.format(self.get_format_view())
     def get_format_view(self):
         return '<a href="{}">' \
-               '<img src="{}" width="200" height="150"/>' \
+               '<img class="url-image" src="{}" width="200" height="150"/>' \
                '</a>'.format(self.url, static(FILE_STUB_URL))

boards/static/css/base.css

@@ -169,3 +169,7 b' textarea, input {'
     border-bottom: dashed 1px;
     cursor: help;
 }
+
+.url-image:hover {
+    filter: invert(100%);
+}