The document discusses the benefits of using Block Element Modifier (BEM) methodology for CSS architecture. It begins with an introduction to BEM, explaining the concepts of blocks, elements, and modifiers. It then discusses some of the practical benefits of BEM such as reducing CSS specificity issues, improving decoupling of HTML and CSS, and enabling automation through predictable class naming. It addresses some potential criticisms of BEM like long class names but argues that BEM can be used effectively on projects of any size. Finally it shares some BEM tools and techniques including approaches for handling multiple modifiers on a single element.

1. The benefits of BEM
CSS
The benefits of BEM CSS - Bob Donderwinkel, 2014 1

2. Who?
• Bob Donderwinkel
• Front-end Developer at Viewbook
• Freelancer at bd creations
The benefits of BEM CSS - Bob Donderwinkel, 2014 2

3. Who?
• Bob Donderwinkel
• Front-end Developer at Viewbook
Our hardheaded senior front-end developer, currently
specialising in responsive HTML, CSS and mobile
• Freelancer at bd creations
The benefits of BEM CSS - Bob Donderwinkel, 2014 3

4. Who?
• Bob Donderwinkel
• Front-end Developer at Viewbook
Our hardheaded senior front-end developer, currently
specialising in responsive HTML, CSS and mobile
• Freelancer at bd creations
Development with Eye for Design
The benefits of BEM CSS - Bob Donderwinkel, 2014 4

5. So what's the gist?
• What is BEM?
• What does BEM solve?
• What have I used BEM for?
• Some semi-interesting BEM tidbits
The benefits of BEM CSS - Bob Donderwinkel, 2014 5

6. So what's the gist?
• What is BEM?
• What does BEM solve?
• What have I used BEM for?
• Some semi-interesting BEM tidbits
Mind you, I have been working with BEM CSS for about half a
year now.
The benefits of BEM CSS - Bob Donderwinkel, 2014 6

7. So what is BEM?
The benefits of BEM CSS - Bob Donderwinkel, 2014 7

8. Block, Element, Modifier
The benefits of BEM CSS - Bob Donderwinkel, 2014 8

9. So what is BEM?
You might just as well call it
Module, Object, Modifier
But then you could be saying something like
I am using MOM
Which would be weird.
The benefits of BEM CSS - Bob Donderwinkel, 2014 9

10. Unified semantic model
for markup, styles, code
and UX
— Smashing Magazine
The benefits of BEM CSS - Bob Donderwinkel, 2014 10

11. What is BEM?
• BEM originated at Yandex
• BEM is a methodology, an abstract way of reasoning about
your interface.
• BEM captures purpose and meaning through it's CSS
classname syntax.
The benefits of BEM CSS - Bob Donderwinkel, 2014 11

12. What is BEM?
BEM is not just for CSS. It is about communicating between
technologies and the people using them.
• Design
• Markup
• Styles
• Code
The benefits of BEM CSS - Bob Donderwinkel, 2014 12

13. Block, Elements and Modifiers
What is that about?
The benefits of BEM CSS - Bob Donderwinkel, 2014 13

14. Block
What is BEM?
• An independent, reusable part of your interface.
• Think: Headers, Menus, Images, etc
• Can contain Elements and other Blocks.
• Can contain one or more Modifiers
<header class='b-header'>
</header>
The benefits of BEM CSS - Bob Donderwinkel, 2014 14

15. Element
What is BEM?
• Belongs to a Block, only has meaning there
• Can contain other Elements and Blocks.
• Think: Header sub-title, Menu item, Image caption, etc
• Can contain one or more Modifiers
<header class='b-header'>
<h1 class='b-header__title'></h1>
<p class='b-header__description'></p>
</header>
The benefits of BEM CSS - Bob Donderwinkel, 2014 15

16. Modifiers
What is BEM?
• Belongs on a Block or Element
• Indicates a state different from the default
• Think: themes, active/inactive state, aligning, etc
• Can also be a key value pair
<header class='b-header b-header_theme_awesome'>
<h1 class='b-header__title b-header__title_large'></h1>
<p class='b-header__description'></p>
</header>
The benefits of BEM CSS - Bob Donderwinkel, 2014 16

17. Modifiers
What is BEM?
And Modifiers are nicely groupable using CSS preprocessors
like SASS/LESS
.b-header{
&_theme_awesome{
background-color: PapayaWhip;
}
&__title {
&_large{
font-size: xx-large;
}
}
}
The benefits of BEM CSS - Bob Donderwinkel, 2014 17

18. BEM CSS syntax
What is BEM?
The official syntax
.b-[block-name]
.b-[block-name]__[element]
.b-[block-name]__[element]_[modifier]
Pretty simple.
- Use only Latin letters, dashes and digits. Not underscores (_)
- Use underscores as the Block, Element and Modifier
separators.
The benefits of BEM CSS - Bob Donderwinkel, 2014 18

19. BEM CSS syntax
What is BEM?
Is this okay?
.b-[block-name]__[element]__[sub-element]
.b-[block-name]_[modifier]__[element]
I have seen some conflicting articles, but probably not.
The benefits of BEM CSS - Bob Donderwinkel, 2014 19

20. BEM CSS syntax
What is BEM?
Or roll your own syntax.
Perhaps because that better suits the CSS code base of a
project. In any case:
• Be consistent
• Keep the Block/Element/Modifier separators unique so you
can use BEM automation tools.
The benefits of BEM CSS - Bob Donderwinkel, 2014 20

21. BEM CSS syntax
So what is BEM?
Most importantly, use meaningful BEM classnames.
If you end up with something like this, it could pretty much
defeat the point.
.b-awesome-gizmo-three__teaser_latest
The benefits of BEM CSS - Bob Donderwinkel, 2014 21

22. What is BEM?
BEM also touches on some well known Object Oriented
Programming concepts.
Don't Repeat Yourself (DRY)
- Blocks are self contained and reusable.
Seperation of Concerns
- Using BEM CSS classes decouples your CSS from your HTML.
The benefits of BEM CSS - Bob Donderwinkel, 2014 22

23. What is BEM?
BEM also touches on some well known Object Oriented
Programming concepts.
Single Responsibility Principle
- Blocks, Element and Modifiers focus on managing just one
thing, themselves.
Open/Closed Principle
- Modifiers often only extend on default styles and behaviour
The benefits of BEM CSS - Bob Donderwinkel, 2014 23

24. So what does BEM CSS solve?
The benefits of BEM CSS - Bob Donderwinkel, 2014 24

25. Chaos (Greek χάοςm
khaos) the formless or
void state preceding the
creation of .. (*)
— * = insert title of your awesome project here
The benefits of BEM CSS - Bob Donderwinkel, 2014 25

26. Seriously, what does using BEM CSS really help with?
CSS can be wonderfully simple and easy to get started with. And
even easier to mess up on the long run.
Legacy CSS can be a royal pain.
We have all been there, or have inherited these kind of
projects to take care of.
The benefits of BEM CSS - Bob Donderwinkel, 2014 26

27. Seriously, what does using BEM CSS really help with?
When projects scale, CSS often does not.
CSS code is easy to append, overwrite or reinvent. That can
turn in to a mess.
It is a bit like growing a new haircut every month, but only
trimming a piece of it.
The benefits of BEM CSS - Bob Donderwinkel, 2014 27

28. It is fun until you
realise you can not
walk away from it.
The benefits of BEM CSS - Bob Donderwinkel, 2014 28

29. So what does BEM CSS solve?
BEM CSS gives you a default aproach for new projects.
• Thinking in Blocks, Elements and Modifiers helps you figure
out what your design is made of.
• BEM helps you getting started coding CSS a little bit quicker
through a standard syntax.
• BEM is about communicating between technologies and
the people using them.
The benefits of BEM CSS - Bob Donderwinkel, 2014 29

30. So what does BEM CSS solve?
For example
- Your design tells you what Blocks, Elements and Modifiers are present.
- You can use these to scaffold up a rough prototype using HTML and CSS.
- You review the prototype to see what behaviour is needed with Javascript.
- The design is tweaked and the prototype is tuned.
- Rinse and repeat.
And you're done..
..Well at least you have a better idea what your project needs
to complete ;)
The benefits of BEM CSS - Bob Donderwinkel, 2014 30

31. Yes, yes.. Can you give me some
pratical reasons to use BEM CSS
The benefits of BEM CSS - Bob Donderwinkel, 2014 31

32. Is there any practical stuff BEM CSS can help with?
What does BEM solve
Single CSS classname perks
Better CSS performance
• Rendering engines evaluate CSS selectors right to left.
• The less they have to evaluate, the faster it renders.
The benefits of BEM CSS - Bob Donderwinkel, 2014 32

33. Is there any practical stuff BEM CSS can help with?
What does BEM solve
My view is that authors should not need to worry about
optimizing selectors (and from what I see, they generally don’t),
that should be the job of the engine.
~ Antti Koivisto
Luckely CSS is the least of your performance worries today.
The benefits of BEM CSS - Bob Donderwinkel, 2014 33

34. Is there any practical stuff BEM CSS can help with?
What does BEM solve
Reduce hell in CSS specificty
• Complex CSS selectors get a higher importance. You have
to match up to this selector or use !important to override it.
• Or find the actual CSS you want to change. But the bigger
the CSS code base, the nastier that can get ;)
Using single CSS classnames makes it easier to rework your
existing CSS code base.
The benefits of BEM CSS - Bob Donderwinkel, 2014 34

35. Is there any practical stuff BEM CSS can help with?
What does BEM solve
Global CSS reset/normalize not needed (preferably)
• Remember BEM Blocks should be independent and re-usable.
A global CSS reset/normalize does not exactly fit
that idea.
Perhaps use something like uncss in your build process to get
only the needed normalize/reset CSS into your Blocks and
Elements.
The benefits of BEM CSS - Bob Donderwinkel, 2014 35

36. Is there any practical stuff BEM CSS can help with?
What does BEM solve
Better HTML/CSS decoupling
• Using HTML element names in your CSS selectors forces
you to update both when only one changes.
• Using just single CSS BEM classnames makes them more
portable to another HTML structure.
The benefits of BEM CSS - Bob Donderwinkel, 2014 36

37. Is there any practical stuff BEM CSS can help with?
What does BEM solve
Project automation through BEM's predictable CSS
classnames
• Yandex has tools if you are using the standard BEM syntax
• CSS preprocessors like SASS and LESS are especially well
suited for generating BEM CSS
• And with build tools like Grunt or Gulp you can custom fit
BEM CSS automation for your own project.
The benefits of BEM CSS - Bob Donderwinkel, 2014 37

38. But is it all utter BEM BLISS?
The benefits of BEM CSS - Bob Donderwinkel, 2014 38

39. Utter BEM BLISS?
What about the CSS cascade?
Yes, using just single CSS classnames can feel a bit too
simplistic at times. But you can use regular CSS allong with
your BEM CSS. Or you can use SASS or LESS to @include or
@extend a CSS library.
@import "my-themes";
&_theme_awesome{
@include theme-more-awesome();
}
The benefits of BEM CSS - Bob Donderwinkel, 2014 39

40. Utter BEM BLISS?
But I hate looking at long and ugly-ish CSS classnames
• True.. no way around that. BEM CSS can be a tad
challenging for the aesthetically inclinded code fashionista.
• But luckely the visitor of website or application will not look
in the source all too often ;)
Doesn't HTML filesize bloat with long CSS classnames?
• Yes, true. But minification and gzipping go a long way.
The benefits of BEM CSS - Bob Donderwinkel, 2014 40

41. Utter BEM CSS BLISS?
And is BEM only useful in larger teams?
• BEM CSS certainly has extra perks in larger teams because
of the meaningful BEM CSS classnames.
• But working solo you can also use the Block, Element and
Modifier approach on a design to get started prototyping
sooner.
The benefits of BEM CSS - Bob Donderwinkel, 2014 41

42. Utter BEM CSS BLISS?
Is BEM not yet another 'framework/methodology/
whatever' to try and get my head around?
• Yes, but it's concept and syntax is pretty straight forward to
get started with and use.
• And BEM can play pretty nicely with other CSS approaches
out there.
The benefits of BEM CSS - Bob Donderwinkel, 2014 42

43. Utter BEM BLISS?
Other CSS approaches
Object Oriented CSS
• Separation of Structure from Skin
• Separation of Containers and Content
In essence OOCSS is about keeping CSS modular so it can be
reused and extended. This is similar to the Block, Element and
Modifier approach.
The benefits of BEM CSS - Bob Donderwinkel, 2014 43

44. Utter BEM BLISS?
Other CSS approaches
Scalable and Modular Architecture for CSS
• Guidelines how you can write and organize your CSS
SMACCS has five types of CSS categories Base, Layout,
Module, State, Theme.
The Module and State categories are simular analogue for the
Block, Element and Modifier approach.
The benefits of BEM CSS - Bob Donderwinkel, 2014 44

45. Utter BEM BLISS?
Other CSS approaches
Web components
- Polymer and Brick
Web Components are a collection of web standards focussed
on delivering self-contained and reusable custom blocks of
HTML, Javascript & CSS.
BEM CSS can be used 'inside' a Web Component just like in
any other project, and with roughly the same benefits.
The benefits of BEM CSS - Bob Donderwinkel, 2014 45

46. Do you have some interesting
BEM CSS tidbits?
The benefits of BEM CSS - Bob Donderwinkel, 2014 46

47. Multi modifer CSS classes
BEM tidbits
Multi modifer CSS classes
- Some Gulp.js which will rework a bit of BEM CSS so you can
use multiple Modifiers in a single BEM class
__block__element_theme-light_size-large
Wow, even longer CSS classnames...!
The benefits of BEM CSS - Bob Donderwinkel, 2014 47

48. Multi modifer CSS classes
BEM tidbits
@bobdonderwinkel we suggest to use classic approach and write
as many classes as needed in DOM tree
@bobdonderwinkel and avoid copypaste with the help of
template engines
— Twitter #b_
Yeah, perhaps not that great an idea afterall. Fun experiment
though.
The benefits of BEM CSS - Bob Donderwinkel, 2014 48

49. kaBEM
BEM tidbits
BEM CSS scaffolding on some steroids
kaBEM is a grunt.js environment for quick scaffolding and
tweaking of HTML with BEM CSS (Block, Element, Modifier).
- See a BEM classname in your CSS and know where to use it in your HTML
- See a BEM classname in your HTML and know where to find it in your CSS files
- See a BEM classname and know which purpose it has
But.. Disclaimer
The benefits of BEM CSS - Bob Donderwinkel, 2014 49

50. kaBEM
BEM tidbits
Disclaimer: I created kaBEM just starting with BEM CSS. So be
mindful of some little hickups that trickeled in. For example
kaBEM uses multi element/modifier BEM CSS classnames.
.b-block__element-1__element-2
.b-block__element_modifiers-1_modifier-2
In hindsight these are a bit of a BEM CSS no-no ;) But no
worries, a new version is on the way.
The benefits of BEM CSS - Bob Donderwinkel, 2014 50

51. BEM User Stories
BEM tidbits
User stories seem like a nice way to get going with BEM even
before you get busy with a design or prototype.
• Sum up what parts should be present (Blocks and Elements)
• Describe how these parts should look & behave (Modifiers)
• Translate these User Stories in BEM CSS classnames
• Get some coffee and start coding
The benefits of BEM CSS - Bob Donderwinkel, 2014 51

52. Okay, round up already
The benefits of BEM CSS - Bob Donderwinkel, 2014 52

53. Rounding up
• Thinking in Block, Elements and Modifiers helps you
interpretate a design quicker and get you started coding
sooner.
• BEM CSS classnames are about communicating, keep them
meaningful.
• BEM CSS classnames are well suited for automation
because of it's default syntax.
The benefits of BEM CSS - Bob Donderwinkel, 2014 53

54. Good reads
Rounding up
• Scaling Down The BEM Methodology For Small Projects
• MindBEMding – getting your head ’round BEM syntax
• Organizing CSS: OOCSS, SMACSS, and BEM
• Generating BEM selectors with CSS preprocessors
The benefits of BEM CSS - Bob Donderwinkel, 2014 54

55. Contact me!
Rounding up
• www.bdcreations.nl
• b.donderwinkel@bdcreations.nl
• Twitter
• Linkedin
The benefits of BEM CSS - Bob Donderwinkel, 2014 55