So I needed to adjust the margins between images and I created a new class (instead of adjusting my gantry-width-25), but in doing so, lost the formatting for other devices...items are not responsive...
Ok, I did find these two files in a previous post:
..\templates\rt_templateName\less\gantry-core.less
..\templates\rt_templateName\less\mediaqueries.less
There was nothing in the gantry-core.less that I noticed regarding width.
I did add ".gantry-width-21," with all the other gantry-width items in the mobile section in the mediaqueries.less file, but still don't see a difference...
I was able to get my gantry-width-45 working properly. I made sure to add the necessary code to gantry-core.less and mediaqueries.less. Apparently, I was missing a comma after my declaration in mediaqueries.less and it was causing the error.
For the gantry-core.less, I just scrolled down to the list of declarations and added the gantry-width-45 with the 45%. Basically the same code as gantry-width-40.
Then, for the mediaqueries.less, there is a line of code that has all of the gantry-width-xx options in it, just make sure to add a comma and place your custom one in that same line.
Originally, I had forgotten the comma, so mine looked like this: ...gantry-width-30, gantry-width-40 gantry-width-45, gantry...
Once the comma was fixed, everything worked fine. I'm currently using a modified version of the Corvus template.
Hope this helps, and let me know if you need anything else.