August 30, 2016

Refactoring CSS: The Three I’s

In a recent interview, I was asked about simple and/or replicable steps to take when refactoring CSS. The topics of legacy, Technical Debt, and refactoring are, for one reason or another, at the front of my mind at the moment, so I thought I would write up a short post on an approach to refactoring CSS (or any language) that I call The Three I’s: Identify, Isolate, Implement.


It’s all well and good knowing that ‘your CSS is a mess’, but which bits specifically? Which parts of your codebase are causing you problems right now? Which ones will be the quickest to refactor? Which parts will provide you with the most benefit once refactored? It is important to identify prime candidates for refactoring.

For example, the CSS for your nav might be cumbersome and hard to work with, but if the nav works correctly, is accessible, and you rarely have to edit the CSS for it, refactoring it will likely not provide you with much immediate value: we can probably afford to leave it as it is for a little while longer. However, your layout/grid system might be incredibly fragmented and inconsistent, it might have cross-browser issues, its responsiveness may have been bolted on as an afterthought, and of course it is probably used extensively and frequently. As a result, you might get a lot of value from tackling that first.

Have a clear idea of which parts of your project should be refactored, if at all.

Tip: Try to limit refactoring work to the scope of single features. It’s much safer to refactor a single feature than it is to refactor your entire naming convention, for example. For further detail on this, and much more, you can see my Refactoring CSS Without Losing Your Mind talk at a number of events throughout the rest of 2016.


Once we have identified candidates for refactoring, we need to isolate them before and during working on them. Suppose we have decided to refactor our layout system first, we should rewrite this in isolation, outside of our project.

In order to do this, open a new jsFiddle, CodePen, etc. and begin work there. Do not refactor features back into a stale codebase, as doing so runs the risk of making use of legacy CSS that may itself be refactored in future. For example, we might be using a traditional reset in the current project, which may be replaced by Normalize.css in future—we don’t want to build our brand new layout system on top of a reset that will be removed in six months time.

Build the new/refactored version of your feature in complete isolation so that you know it is well encapsulated, and it’s not making use of any legacy.


The final step is to implement your refactored feature. Copy and paste the jsFiddle CSS into the relevant part of your project, and see what happens. 90% of the time, you’ll find that there are some problems: conflicts with existing CSS, naming collisions, existing styles leaking into your new code, etc.

We tackle these details at implementation stage, and we need to give careful consideration as to where we place the fixes. If the fix solves a problem with the layout system itself, it is usually best to place the fix in the layout system’s partial. If the fix addresses problems arising from conflicts with legacy code, it is often best to place it in a shame.css file. This keeps the legacy fix away from greenfield CSS, meaning it will be much easier to remove once we’ve refactored whatever legacy was causing the problem in the first place.

Move the refactored feature back into the project and tidy things up here.

In short:

  1. Identify sensible candidates for refactoring: not all legacy is born equal.
  2. Isolate the feature in order to rebuild it: do not lean on out of date code.
  3. Implement the refactored feature into the project: do any cleanup work at this point, and in the right place(s).