I can only load sigma.require.js

Apparently, I can only load: node_modules/sigma/build/sigma.require.js
as trying to load things in the src directory commit another sigma to the global window object.

Getting error that the stylesheet cannot be loaded and the graph is not rendered with require...

See sigma.js issue https://github.com/jacomyal/sigma.js/issues/186  and look for some tests for the sigma function.

Also, here is webpack: https://github.com/jacomyal/sigma.js/issues/730

Here is one with browserify: https://github.com/jacomyal/sigma.js/issues/680

How to use bower: https://github.com/jacomyal/sigma.js/issues/439

Browserify: http://browserify.org/