Super simple node script to find CSS that is no longer in use. The results should be considered as safe as a global find and replace (not very), so use your judgement

find-dead-css.js

var walk                    = require('walk');
var fs                      = require('fs');
var classesOrIds            = [];
var viewsAndTemplates       = []
var walkers                 = [];
var maybeUnusedClassesOrIds = [];
var compleWalkersCount      = 0;
var classesToFileMap        = {}

// Calback Function every time a walker ends
var onWalkerEnd     = function(walkerId) {

    compleWalkersCount++

    // All walkers are complete
    // We can only perform this logic once we have all the data
    if (compleWalkersCount === walkers.length) {

        // Loop through all the classes or IDs
        for (i = 0; i < classesOrIds.length; i++) {

            // The class or ID we are looking for
            classOrId = classesOrIds[i]

            // Loop through all the views and Templates
            for (ii = 0; ii < viewsAndTemplates.length; ii++) {

                // We found this class or ID in a view or template
                if (viewsAndTemplates[ii].indexOf(classOrId.substring(1)) > -1) {
                    break;
                }

                // We didnt find this class or id inside any view or template
                if (ii === viewsAndTemplates.length -1) {
                    maybeUnusedClassesOrIds.push(classOrId)
                }

            }

        }

        console.log("Found " + classesOrIds.length + " CSS classes or ids");
        console.log(maybeUnusedClassesOrIds.length + " of those might not be in use anymore:");
        console.log("  ");

        // Log each class or ID that we couldnt find
        maybeUnusedClassesOrIds.forEach(function(classOrId) {

            logString = classOrId

            // Right Pad the string so we a nice column of locations
            for (i = 0; i < 40 - classOrId.length; i++) {
                logString += " "
            }

            console.log(logString + classesToFileMap[classOrId]);
        })

    }

};

// Gets all the CSS Classes or Ids
walkers.push(walk.walk('./app/assets/css', { followLinks: false }).on('file', function(root, stat, next) {

    // Opens each file
    // Note this will open other files as well
    fs.readFile(root + '/' + stat.name, 'utf8', function(error, data) {

        // Assume the CSS is unminified
        // If so we assume that each selector starts on a new line
        data.split('\n').forEach(function(line) {

            // Find Class selectors
            // Assume that lines starting with a . are a class selectors
            // Note this won't catch instances of element.class
            if (line[0] === '.') {
                name = line.split('.')[1].split(' ')[0].split(':')[0].split('\t')[0].split(',')[0].split('[')[0];

                if (classesOrIds.indexOf("." + name) === -1) {
                    classesOrIds.push("." + name);
                    classesToFileMap["." + name] = root + '/' + stat.name;
                }

            }

            // Find ID selectors
            // Assume that lines starting with a # are ID selectors
            // Note this won't catch instances of element#id
            if (line[0] === '#') {
                name = line.split('#')[1].split(' ')[0].split(':')[0].split('\t')[0].split(',')[0].split('[')[0].split('.')[0];

                if (classesOrIds.indexOf("#" + name) === -1) {
                    classesOrIds.push("#" + name);
                    classesToFileMap["#" + name] = root + '/' + stat.name;
                }

            }

        })

        next();

    });

}).on('end', onWalkerEnd));

// Gets all the mustache templates
walkers.push(walk.walk('./app/templates', { followLinks: false }).on('file', function(root, stat, next) {

    // Read & save the content of the mustache template
    // We'll check this for classes or ids later
    fs.readFile(root + '/' + stat.name, 'utf8', function(error, data) {
        viewsAndTemplates.push(data);
        next();

    });

}).on('end', onWalkerEnd));


// Gets all the views/components
walkers.push(walk.walk('./app/coffeescript/views', { followLinks: false }).on('file', function(root, stat, next) {

    // Read & save the content of the view
    // We'll check this for classes or ids later
    fs.readFile(root + '/' + stat.name, 'utf8', function(error, data) {
        viewsAndTemplates.push(data)
        next();

    });

}).on('end', onWalkerEnd));