Hi, I use Coda 2 also
Install the Text Tools 2 plugin into coda:
Unzip and install that plugin. Select all the CSS in the file, right click and from context menu, select Scripts-->Lowercase
Now all items in css are lowercase.
I am trying to remember if Coda 2 has native lowercase conversion, but since I use so many Coda 2 plugins, I find it easier just to use those... you should be able to download the plugin I listed, unzip that and just double click to install...
Good luck mate!