General CSS notes, advice and guidelines

In working on large, long running projects , it is important that we all work in a unified way in order to, among other things: - Keep stylesheets maintainable - Keep code transparent and readable - Keep stylesheets scalable

There are a variety of techniques we must employ in order to satisfy these goals.

CSS Document Anatomy

No matter the document, we must always try and keep a common formatting. This means consistent commenting, consistent syntax and consistent naming.


Table of contents

At the top of stylesheets, I maintain a table of contents which will detail the sections contained in the document, for example:

/* ================================= */
/* ------  TABLE of CONTENTS ------- */
/* --------------------------------- */
/* ------- 1. General Typography --- */
/* ------- 2. General page css ----- */
/* ------- 3. Library -------------- */
/* ------- 4. General panels ------- */
/* ------- 5. Header --------------- */
/* ------- 6. Footer --------------- */
/* ------- 7. Content Specific ----- */
/* ================================= */

This will tell the next developer(s) exactly what they can expect to find in this file. Each item in the table of contents maps directly to a section title.

If you are working in one big stylesheet, the corresponding section will also be in that file. If you are working across multiple files then each item in the table of contents will map to an include which pulls that section in.

Color Swatches

At the top I keep a list of colors that I will be using for various elements , and I grab these colors from from the mock-ups keep here so that I won't have to search for the colors each time.

/* ----------------------swatches ---------------------- */
/*  page background (blue)             => #7ca8d3        */
/*  top-panel slideshow bg (dark blue) => #005596        */
/*  title text (light blue)            => #3f7cab        */
/*  preface bg (grey)                  => #d0d0d0        */
/*  text color (light grey)            => #4d4d4d        */
/* ===================================================== */

If you are working across multiple, included stylesheets, start each of those files with a section title and there is no need for any carriage returns.

Section titles

The table of contents would be of no use unless it had corresponding section titles. Denote a section thus:

/* ================================= */
/* ------  GENERAL TYPOGRAPHY ------ */
/* ================================= */

If you are working across multiple, included stylesheets, start each of those files with a section title and there is no need for any carriage returns.

Source order

Try and write stylesheets in specificity order. This ensures that you take full advantage of inheritance and CSS’ first C; the cascade.

A well ordered stylesheet will be ordered something like this: - Reset – ground zero. - Elements – unclassed h1, unclassed ul etc. - Objects and abstractions — generic, underlying design patterns. - Components – full components constructed from objects and their extensions.

This means that—as you go down the document—each section builds upon and inherits sensibly from the previous one(s). There should be less undoing of styles, less specificity problems and all-round better architected stylesheets. For further reading I recommend Jonathan Snook’s SMACSS.

Anatomy of rulesets

    [<- -="" declaration="">]

I have a number of standards when structuring rulesets. - 2 space indented - Multi-line - Indent vendor prefixed declarations so that their values are aligned - Indent our rulesets to mirror the DOM [if possible] - Always include the final semi-colon in a ruleset

A brief example:

    border:1px solid #BADA55;
        margin-left: -10px;

Here we can see that .block-heading must be a child of .block as we have indented the .block-heading ruleset one level deeper than .block. This is useful information to developers that can now be gleaned just by a glance at the indentation of our rulesets. One exception to our multi-line rule might be in cases of the following:

.t10    { width:10% }
.t20    { width:20% }
.t25    { width:25% }       /* 1/4 */
.t30    { width:30% }
.t33    { width:33.333% }   /* 1/3 */
.t40    { width:40% }
.t50    { width:50% }       /* 1/2 */
.t60    { width:60% }
.t66    { width:66.666% }   /* 2/3 */
.t70    { width:70% }
.t75    { width:75% }       /* 3/4*/
.t80    { width:80% }
.t90    { width:90% }

Naming conventions

For the most part I simply use hyphen delimited classes (e.g. .foo-bar, not .foo_bar or .fooBar), however in certain circumstances we can use BEM (Block, Element, Modifier) notation.

BEM is a methodology for naming and classifying CSS selectors(this should be applied to the classes we are giving to panes and block) in a way to make them a lot more strict, transparent and informative.

The naming convention follows this pattern:


.block represents the higher level of an abstraction or component. .block__element represents a descendent of .block that helps form .block as a whole. .block--modifier represents a different state or version of .block. An analogy of how BEM classes work might be:


Here we can see that the basic object we’re describing is a person, and that a different type of person might be a woman. We can also see that people have hands; these are sub-parts of people, and there are different variations, like left and right.

We can now namespace our selectors based on their base objects and we can also communicate what job the selector does; is it a sub-component (__) or a variation (--)?

BEM looks a little uglier, and is a lot more verbose, but it grants us a lot of power in that we can glean the functions and relationships of elements from their classes alone. Also, BEM syntax will typically compress (gzip) very well as compression favours/works well with repetition.

Regardless of whether you need to use BEM or not, always ensure classes are sensibly named; keep them as short as possible but as long as necessary. Ensure any objects or abstractions are very vaguely named (e.g. .ui-list, .media) to allow for greater reuse. Extensions of objects should be much more explicitly named (e.g. .user-avatar-link). Don’t worry about the amount or length of classes; gzip will compress well written code incredibly well.


we should use following commenting style :

 * This is a docBlock style comment
 * This is a longer description of the comment, describing the code in more
 * detail. We limit these lines to a maximum of 80 characters in length.
 * We can have markup in the comments, and are encouraged to do so:
 *     Lorem
 * We do not prefix lines of code with an asterisk as to do so would inhibit
 * copy and paste.

You should document and comment our code as much as you possibly can, what may seem or feel transparent and self explanatory to you may not be to another dev. Write a chunk of code then write about it.

NOTE : You should never qualify your selectors; that is to say, we should never write ul.nav{} if you can just have .nav. Qualifying selectors decreases selector performance, inhibits the potential for reusing a class on a different type of element and it increases the selector’s specificity. These are all things that should be avoided at all costs.

However, sometimes it is useful to communicate to the next developer(s) where you intend a class to be used. Let’s take.product-page for example; this class sounds as though it would be used on a high-level container, perhaps the html or bodyelement, but with .product-page alone it is impossible to tell.

By quasi-qualifying this selector (i.e. commenting out the leading type selector) we can communicate where we wish to have this class applied, thus:


We can now see exactly where to apply this class but with none of the specificity or non-reusability drawbacks.

Other examples might be:


Here we can see where we intend each of these classes to be applied without actually ever impacting the specificity of the selectors.

Writing CSS

The previous section dealt with how we structure and form our CSS; they were very quantifiable rules. The next section is a little more theoretical and deals with our attitude and approach.

Building new components

When building a new component write markup before CSS. This means you can visually see which CSS properties are naturally inherited and thus avoid reapplying redundant styles. By writing markup first you can focus on data, content and semantics and then apply only the relevant classes and CSS afterwards.


I work in an OOCSS manner; I split components into structure (objects) and skin (extensions). As an analogy (note, not example) take the following:



We have several types of room in a house, but they all share similar traits; they all have floors, ceilings, walls and doors. We can share this information in an abstracted .room{} class. However we have specific types of room that are different from the others; a kitchen might have a tiled floor and a bedroom might have carpets, a bathroom might not have a window but a bedroom most likely will, each room likely has different coloured walls. OOCSS teaches us to abstract the shared styles out into a base object and then extend this information with more specific classes to add the unique treatment(s).

So, instead of building dozens of unique components, try and spot repeated design patterns across them all and abstract them out into reusable classes; build these skeletons as base ‘objects’ and then peg classes onto these to extend their styling for more unique circumstances.

If you have to build a new component split it into structure and skin; build the structure of the component using very generic classes so that we can reuse that construct and then use more specific classes to skin it up and add design treatments.


Grid systems should be thought of as shelves. They contain content but are not content in themselves. You put up your shelves then fill them with your stuff. By setting up our grids separately to our components you can move components around a lot more easily than if they had dimensions applied to them; this makes our front-ends a lot more adaptable and quick to work with.

You should never apply any styles to a grid item, they are for layout purposes only. Apply styling to content inside a grid item. Never, under any circumstances, apply box-model properties to a grid item.


Shorthand CSS needs to be used with caution.

It might be tempting to use declarations like background:red; but in doing so what you are actually saying is ‘I want no image to scroll, aligned top-left, repeating X and Y, and a background colour of red’. Nine times out of ten this won’t cause any issues but that one time it does is annoying enough to warrant not using such shorthand. Instead usebackground-color:red;.

Similarly, declarations like margin:0; are nice and short, but be explicit. If you actually only really want to affect the margin on the bottom of an element then it is more appropriate to use margin-bottom:0;.

Be explicit in which properties you set and take care to not inadvertently unset others with shorthand. E.g. if you only want to remove the bottom margin on an element then there is no sense in setting all margins to zero with margin:0;.

Shorthand is good, but easily misused.


A quick note on IDs in CSS before we dive into selectors in general.

Avoid use of IDs in CSS.

They can be used in your markup for JS and fragment identifiers but use only classes for styling. Use it only for very specific styles.

Classes come with the benefit of being reusable (even if we don’t want to, we can) and they have a nice, low specificity. Specificity is one of the quickest ways to run into difficulties in projects and keeping it low at all times is imperative. An ID is 255 times more specific than a class, so never ever use them in CSS ever.


Keep selectors short, efficient and portable.

Heavily location-based selectors are bad for a number of reasons. For example, take .sidebar h3 span{}. This selector is too location-based and thus we cannot move that span outside of a h3 outside of .sidebar and maintain styling.

Selectors which are too long also introduce performance issues; the more checks in a selector (e.g. .sidebar h3 span has three checks, .content ul p a has four), the more work the browser has to do.

Make sure styles aren’t dependent on location where possible, and make sure selectors are nice and short.

Selectors as a whole should be kept short (e.g. one class deep) but the class names themselves should be as long as they need to be. A class of .user-avatar is far nicer than.usr-avt.

Remember: classes are neither semantic or insemantic; they are sensible or insensible! Stop stressing about ‘semantic’ class names and pick something sensible and futureproof.

Over-qualified selectors

As discussed above, qualified selectors are bad news.

An over-qualified selector is one like You could probably get the same effect from just using .promo. Of course sometimes you will want to qualify a class with an element (e.g. if you have a generic .error class that needs to look different when applied to different elements (e.g. .error{ color:red; } div.error{ padding:14px; })), but generally avoid it where possible.

Another example of an over-qualified selector might be ul.nav li a{}. As above, we can instantly drop the ul and because we know .nav is a list, we therefore know that anya must be in an li, so we can get ul.nav li a{} down to just .nav a{}.

Selector performance

Whilst it is true that browsers will only ever keep getting faster at rendering CSS, efficiency is something you could do to keep an eye on. Short, unnested selectors, not using the universal (*{}) selector as the key selector, and avoiding more complex CSS3 selectors should help circumvent these problems.

CSS selector intent

Instead of using selectors to drill down the DOM to an element, it is often best to put a class on the element you explicitly want to style. Let’s take a specific example with a selector like.header ul{}…

Let’s imagine that ul is indeed the main navigation for our website. It lives in the header as you might expect and is currently the only ul in there; .header ul{} will work, but it’s not ideal or advisable. It’s not very future proof and certainly not explicit enough. As soon as we add another ul to that header it will adopt the styling of our main nav and the the chances are it won’t want to. This means we either have to refactor a lot of code or undo a lot of styling on subsequent uls in that .header to remove the effects of the far reaching selector.

Your selector’s intent must match that of your reason for styling something; ask yourself ‘am I selecting this because it’s a ulinside of .header or because it is site’s main nav?’. The answer to this will determine your selector.

Make sure your key selector is never an element/type selector or object/abstraction class. You never really want to see selectors like.sidebar ul{} or .footer .media{} in our theme stylesheets.

Be explicit; target the element you want to affect, not its parent. Never assume that markup won’t change. Write selectors that target what you want, not what happens to be there already.


It is okay to use !important on helper classes only. To add !important preemptively is fine, e.g..error{ color:red!important }, as you know you will always want this rule to take precedence.

Using !important reactively, e.g. to get yourself out of nasty specificity situations, is not advised. Rework your CSS and try to combat these issues by refactoring your selectors. Keeping your selectors short and avoiding IDs will help out here massively.

Magic numbers and absolutes

A magic number is a number which is used because ‘it just works’. These are bad because they rarely work for any real reason and are not usually very futureproof or flexible/forgiving. They tend to fix symptoms and not problems.

For example, using .dropdown-nav li:hover ul{ top:37px; } to move a dropdown to the bottom of the nav on hover is bad, as 37px is a magic number. 37px only works here because in this particular scenario the .dropdown-nav happens to be 37px tall.

Instead you should use .dropdown-nav li:hover ul{ top:100%; } which means no matter how tall the .dropdown-nav gets, the dropdown will always sit 100% from the top.

Every time you hard code a number think twice; if you can avoid it by using keywords or ‘aliases’ (i.e. top:100% to mean ‘all the way from the top’) or—even better—no measurements at all then you probably should. Every hard-coded measurement you set is a commitment you might not necessarily want to keep.

Conditional stylesheets

IE stylesheets can, by and large, be totally avoided. The only time an IE stylesheet may be required is to circumvent blatant lack of support (e.g. PNG fixes).

As a general rule, all layout and box-model rules can and will work without an IE stylesheet if you refactor and rework your CSS. This means you never want to see or other such CSS that is clearly using arbitrary styling to just ‘make stuff work’.


If you run into a CSS problem take code away before you start adding more in a bid to fix it. The problem exists in CSS that is already written, more CSS isn’t the right answer!

Delete chunks of markup and CSS until your problem goes away, then you can determine which part of the code the problem lies in.

It can be tempting to put an overflow:hidden; on something to hide the effects of a layout quirk, but overflow was probably never the problem; fix the problem, not its symptoms.