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Front End Development Guidelines

An ongoing, continually updated, repository of my personal front end development guidelines

These guidelines utilize the following principles:

  • Atomic Design
  • Object-oriented SCSS for modular development
  • CSS guidelines / ITCSS scss structure
  • Loosely follows BEM to create clear CSS components but with less parent element name repetition and allowing low-level nesting.

Updates coming soon / To do

  • z-index table usage with variables
  • Harry Roberts - 5 software development principles from CSS for Software Engineers for CSS Developers
    • Dry / single source of truth - mixins and variables for easier maintenence.
    • The single responsibility principle - flexible atomic-like classes.
    • Separation of concerns - do not couple markup and HTML, this creates inherent fragility.
    • Immutability - utility classes should not be mutated, split into two classes if needed.
    • Cyclomatic Complexity - specificity is like if statements, don't nest deeply, keep it simple.
    • The open/closed principle - 'open for extension, closed for modification', don't change legacy code directly, instead use modifiers.
    • Orthogonality - using component based CSS means components can be moved around with consistent results, creating a flexible modular system.
  • Using @at-root to keep component encapsulation
  • Use mixins - not extend to avoid code bloat
  • Component based media queries - link to blog
  • Accessibility guidelines
  • Media query usage instructions
  • MQ packer - reduce media queires in output
  • Performance
    • server requests - combine + minify
    • animation - jank free
    • compositor layers - translate, will change
    • svg
    • image sprites

Brad Frost's Atomic Design and Harry Robert's CSSGuidlines / ITCSS share the same fundamental approach - begin with simple elements / atoms and building up to complex groups of elements / molecules. This works in favor of the cascade and reduces CSS specificity issues and helps to create a truly flexible, modular, interface system.

Further Reading

Harry Roberts and Brad Frost have strongly influenced the guidelines set out below and I highly recommend giving them a read.

Front End Guidelines

Why have guidelines?

  • Disorganised CSS structures make future updates very time ineffective and difficult
  • Updating poorly structured CSS can lead to unexpected style changes across the website, which may even break layout or prevent functionality.
  • Clear CSS structures speed up development
  • Guidelines help get multiple developers work in the same way to keep code bases consistent, making it easier for developers to move projects.


The CSS should aim to be object orientated to create reusable, flexible classes which make future updates easy and logical. Utilize component based css inline with an atomic design methodology.

Main objectives of CSS

  • Component driven
  • Object Orientated
  • Maintainable

Why used component based CSS?

When building interfaces we are creating a system of elements and components that will be used in various combinations. If we keep this in mind we can create a truly fluid and flexible interface system - much like the brilliant Brad Frost - Atomic Design approach. I've written about how atomic / component driven design can transition easily into component based css for better, easier development, see the article here.

BEM or nested.

BEM is a popular approach to managing CSS on large scale projects. A BEM approach to a component would be like this:

.car {}
    .car__wheel {}
    .car__door {}

If we dont use BEM we could we could use nesting for child elements:

.car {
    .wheel {}
    .door {}

To use BEM or not usually depends on project scale. It is particularly useful for large projects allowing multiple devs to work in the same way to keep the codebase consisent.

##Nesting and specificity Specificity can cause issues when working with the cascade, but if component nesting is kept low (ideally no more than 3) and clear, it will cause minimal problems.

BEM approach encourages having a unique class for every element, keeping all elements at the root of the cascade, eliminating any cascade entirely.

Class names

Classe names are all lower case and use underscores for spacing:

<header class="site_header"></header>

Modifier classes use the element's class name with an added double hyphen followed by the modifier name. Use 3 spaces before modifiers for readability and modifier class names come last within the class list.:

<div class="modal   modal--small"></div>

Context vs component / element styles

Implementation styles are based on context, visual styles are based on component / element. Style elements based on what they are - not where they are. Style code should be based on the component. Implementation code should be based on thier context.

For example, if a button is in a component in which the button needs to be floated right, it is due to being inside the parent component. The button styling doesnt need modifying. Simply reference the button inside of the compnent class and add the implementation classes.

A button modifier class in this situation would be another option, although it may create unneeded additional markup, as well as making future style modifications within layout changes more difficult.

Content agnostic class names

Component class names should not be tied to the content inside the component. For example using the the class name welcome_message would not be ideal. As that layout / component could be used elsewhere for other purposes a more appropriate class name would be message.

Avoid use of IDs

IDs have the highest specificity of any CSS selector and as a result they cause issue with overwriting styles in the cascade. Avoid using any IDs. Sometimes developers will add an ID to an element for the sole purpose of referencing the ID in javascript. However this isnt neccessary, instead use a class and reference the element using getElementsByClassName("class_name")[0]; (note 'ClassName' is beneficial over 'ClassList' due to it's wider browser support).

Quasi-Qualified Selectors

ul.nav {} Here we can see that the .nav class is meant to be used on a ul element, and not on a nav. By using quasi-qualified selectors we can still provide that information without actually qualifying the selector
/*ul*/.nav {}

Javascipt hooks

All javascript hooks should be prefixed with 'js_'. for example:

<button class="btn js_open_modal"></button>

Toggle classes for state changes. Do not toggle data attributes for state changes:

A common practice is to use data-* attributes as JS hooks, but this is incorrect. data-* attributes, as per the spec, are used to store custom data private to the page or application (emphasis mine). data-* attributes are designed to store data, not be bound to.

CSS structure

 * Global...............Globally-available variables, mixins and config.
 * Gloablly availible settings. Config switches. Brand colors, mixins etc
 * Normalize.css........A level playing field.
 * Box-sizing...........Better default `box-sizing`.
 * Ground zero styles. Low specificty. Far-reaching. Resets, noramlize etc
 * Headings.............H1–H6 styles.
 * unclassed HTML elements - ul, p, a, buttons, input, textarea, select, blockquote,
 * Wrappers.............Wrapping and constraining elements.
 * OOCSS. Design patterns. No cosmetics. Begin using classes exclusively. Agnostically named (eg ui_list)
 * Page-head............The main page header.
 * Page-foot............The main page footer.
 * Buttons..............Button elements.
 * Designed pieces of UI. Still only using classes. Explicitly named.
 * Optional - Theme Layer 
 * Optional - A/B Test layer
 * Text.................Text helpers.
 * overides, utiliies and helpers, 
 * affect one piece of the DOM at a time
 * usually carry important

CSS titles

All section titles are listed as:

Section Title

Section subtitles listed as:


##CSS Components CSS is to be structured in modular, component based blocks. This means that all styles for individual components are kept in one place for easier edits and maintainability.

/*----------- Hero -------------*/
.hero { width: 100%; height: 400px; position: relative;
    .callout { position: absolute; right: 10%; bottom: 10%; width: 380px; height: 300px; background: #0E1E3F; color: white; overflow: hidden; padding: 2rem;
        h2 { margin-top: 0; font-size: 4rem; color: white; }
        p { color: yellow; font-weight: bold; margin: 1rem 0; }
        a { color: yellow; font-weight: bold;}

    &.hero--callout_left {
        .callout { right: auto; left: 10%; }

    @media (max-width:830px){
        .callout {
            width:100%; right:0; left:0; bottom:0; top:auto; height:auto;
            h2 {font-size: 3rem; }
            p {margin: 1rem 0; }
            a {}

HTML Markup


Use appropriate semantic elements where possible. If unfamiliar with semantic HTML please see here - HTML5 Semantics – Smashing Magazine

3 spaces before modifiers for readability, and odifiers come last within the class name list:

<div class="modal   modal--small"></div>

Meaningful use of white space

As with our rulesets, it is possible to use meaningful whitespace in your HTML. You can denote thematic breaks in content with five (5) empty lines, for example:

<header class="page_head">

<main class="page_content">


An ongoing, continually updated, repository of my personal front end development guidelines







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