With solidified syntax and great browser support, flexbox, the CSS layout module that can make your layouts more flexible and responsive with ease, is finally ready to be used in your real-world work. We’ll talk about the when, what, and how of using flexbox today: when it’s a great choice use flexbox (and when not to), what UI and UX problems it can help you solve, and how to add it to your layouts in a robust way that doesn’t harm non-supporting browsers or accessibility. You’ll learn a step-by-step process for deciding on and deploying flexbox, with lots of examples along the way of flexbox in the wild.

1. Flexbox
Zoe Mickley Gillenwater @zomigiCSS Summit
July 2016
TODAY
USING

2. I work for
Psst…you can too: www.workingatbooking.com

3. My portfolio site from 2000

4. My portfolio site from 2000

5. tables
positioning
floats
inline-block
table-cell
flexbox
grid
multi-column
exclusions
shapes
regions
flexbox

6. when
what
flexbox
how

7. Deciding when to use and not use flexbox
WHEN
¨ 1.

8. What browsers do I need to
support?
Don’t ask yourself this—it’s irrelevant here
(IMO)

9. Flexbox has 96.8% coverage worldwide
We support IE 7-9 at Booking, but still use flexbox as
progressive enhancement.

10. Do I want to create a layout in
1 dimension (row OR column)
or 2 dimensions?
Hat-tip to Rachel Andrew:
https://rachelandrew.co.uk/archives/2016/03/30/should-i-use-grid-or-flexbox/

11. Flexbox is not a grid
¨ Not meant for or great at whole page layout
¨ Flex items only care about space in their
own row/column
¨ They don’t care about lining up in the other
dimension

12. Demo by Rachel Andrew: http://codepen.io/rachelandrew/pen/YqqdXL

13. Flexbox is best for:
¨ UI components
¨ Simple whole page layouts (not grid-based)
¨ Enhancing a complex layout’s alignment,
spacing, etc. (not controlling placement)

15. Do I need my content to
dictate sizing and placement,
or do I need to control these?

16. Content determines
boxes’ size and
placement
(Mega-useful when
content is unknown and
variable, or readability is
a top priority.)
Structure determines
content’s size and
placement
(P.S. Flexbox can do this
too, if you want. It’s just
the reverse that doesn’t
work so well.)
Flexbox Grids

17. Does flexbox offer me anything
I can’t already get
from an existing layout method?

18. New things flexbox offers
¨ Content-driven, unit-less sizes
¨ Content-driven, media-query-less layout changes
¨ Mixed-unit layouts
¨ Equal-height columns
¨ Vertical centering and other alignments
¨ Spacing out or stretching items to fill unknown width/height
¨ Combining content wrapping and block wrapping
¨ Pinning items without overlaps
¨ Visual order different than HTML/reading order

19. Components flexbox can enhance and
UI/UX problems it can help you solve
WHAT
¨ 2.

20. content-driven, unit-less sizes

21. How big do I make this thing?

22. %
em/rem
vw/vh

23. Relative units of measurement
are your best guess at the
ideal, but they’re still a guess.

24. Flexbox gets us closer to the
ideal, because it lets us design
without units.

25. Example: a responsive form
from http://jobs.theguardian.com/

26. My copy of that form
Same floats, same percentage widths

27. The trouble with explicit sizing
Since the select and button are sized by a
percentage, not sized automatically by their
content, this can happen:
Box too small for its content Box too big for its content

28. Use the flex property instead
Tells browser starting size (including content
size) and whether item can grow or shrink
width: 33.333%
flex: auto
Fill up remaining space
width: 16.666%
flex: none
Size to content exactly

29. Form fields are a pain in the butt
The fields and button don’t all match each
other exactly in height

30. Fix alignment with flexbox
Turn each field wrapper into flex container so
field inside will stretch to match height of line:
.flexbox .jobs-form_field-wrapper {
display: flex;
align-items: stretch; /* default */
width: auto;
}
Fields misaligned without flexbox Fields match height due to align-items

31. Smarter sizing
Non-flexbox
Flexbox enhanced

32. Content-driven sizing on Booking.com
Last year’s sidebar searchbox design, with
fixed-width select fields

33. Content-driven sizing on Booking.com
Non-flexbox Flexbox enhanced

34. Content-driven sizing on Booking.com
.sb-dates {
display: flex;
}
.sb-dates__icon {
flex: 0 0 23px;
}
.sb-dates__select-day {
flex: 1 0 auto;
margin: 0 6px;
}
.sb-dates__select-month {
flex: 1 1 auto;
}
flex container
main axis
flex items

35. Defining the flex property
flex-grow
how much flex
item will grow
relative to
other items if
extra space is
available
(proportion
of extra space
that it gets)
flex-shrink
how much item
will shrink
relative to others
if there is not
enough space
(proportion of
overflow that
gets shaved off)
flex-basis
the initial
starting size
before free
space is
distributed
(any standard
width/height
value, including
auto)

36. Translating the flex property
.sb-dates {
display: flex;
}
.sb-dates__icon {
flex: 0 0 23px;
}
.sb-dates__select-day {
flex: 1 0 auto;
margin: 0 6px;
}
.sb-dates__select-month {
flex: 1 1 auto;
}
Start out 23px wide, and don’t grow
or shrink further
Start out sized to your content, then
grow with 1 share of any extra space
available, but don’t ever shrink
Start out sized to your content, then
grow with 1 share of extra space, but
if there’s an overflow shrink

37. Mixed-unit layout is easier with
calc(), but not even it can do:
calc(100% - 23px - the width of
the day field in Greek)

38. Taking advantage of variable space
Task: add a
message about
low availability
of the room
price shown:
“We have only X
left on our site!”
How about right here
in this lovely big gap?

39. Taking advantage of variable space
Problem: the gap
is not always big
enough to hold a
sentence of text

40. Taking advantage of variable space
Solution: use
flexbox to place
text beside price
when space
allows; otherwise,
it can wrap below
price

41. Progressive enhancement
Non-flexbox Flexbox enhanced

42. Content-driven layout change
2 columns 3 columns

43. RWD content-driven layout change
Narrow: 1 column Wide: 2 columns

44. RWD content-driven layout change
.article-header {
display: flex;
flex-flow: row wrap;
margin-left: -20px;
}
.article-header-image {
flex: 1 1 320px;
padding-left: 20px;
}
When 320px + 20em can fit together, layout shifts
to 1 row/2 columns
.article-header-text {
flex: 1 1 20em;
padding-left: 20px;
}

45. Layout change without media query
1. Let the blocks wrap and stack when needed:
.article-header {
display: flex;
flex-direction: row;
flex-wrap: wrap;
}
/* default */

46. Layout change without media query
2. Size the blocks to control their wrapping
point:
.article-header-image {
flex: 1 1 320px;
padding-left: 20px;
}
.article-header-text {
flex: 1 1 20em;
padding-left: 20px;
}

47. Stretching to fill unknown width/height
flex: 1 1 auto
align-content:
space-between

48. Improved wrapping in RWD layout
With float or text-align With flex or justify-content

49. Flexbox is great for spacing
and aligning stuff, especially
shifting content in RWD.

50. Demo: full-width nav bar
¨ All links on same line
¨ First link flush left, last link flush right
¨ Equal spaces between all links

51. Trying display:table-cell
J All links on same line
J First link flush left, last link flush right
L Equal spaces between all links

52. Spacing with table-layout:fixed

53. Starter centered nav bar, no flexbox
.menu-list {
margin: 0;
padding: 0;
list-style: none;
text-align: center;
}
http://codepen.io/zomigi/pen/vKjbbY/
.menu-list-item {
display: inline-block;
padding: 16px 32px;
}

54. Enhanced to full-width with flexbox
.menu-list {
display: flex;
justify-content: space-between; /* equally spaces items across width */
margin: 0;
padding: 0;
list-style: none;
text-align: center; /* fallback */
}
.menu-list-item {
display: inline-block; /* fallback */
padding: 0 .5em; /* fallback */
}

55. Combine with inline-block
Non-flexbox
fallback version
Flexbox version

56. This works vertically too.

57. Demo: full-height menu

58. Demo: full-height menu
.menu-list {
display: flex;
flex-direction: column;
justify-content: space-between;
}
.menu-list-item {
height: 100%;
display: flex;
align-items: center;
}
.menu-list {
display: flex;
flex-direction: column;
}
.menu-list-item {
flex: 1 0 auto;
display: flex;
align-items: center;
}
justify-content version flex version

59. Demo: full-height menu
.menu-list {
display: flex;
flex-direction: column;
justify-content: space-between;
}
.menu-list-item {
height: 100%;
display: flex;
align-items: center;
}
.menu-list {
display: flex;
flex-direction: column;
}
.menu-list-item {
flex: 1 0 auto;
display: flex;
align-items: center;
}
justify-content version flex version

60. Flexbox can also enhance
visual ordering.

61. order
integer to specify flow order of flex items
0
0
0
default source order 0
0
1
0
0
re-ordered 0
0
0
0
-1
re-ordered 0
0
2
1
0
re-ordered 1
0

62. Reorder for good, not evil.

63. Demo: moving a photo on mobile

64. Demo: moving a photo on mobile
Desktop: HTML order (no flexbox)Mobile: reordered

65. Use flexbox order in mobile styles
.recipe {
display: flex;
flex-direction: column;
}
.recipe figure {
order: -1; /* before all items with default order: 0 */
}
.recipe figure img {
width: 100%;
}

66. Turn off flexbox in desktop styles
@media screen and (min-width:800px) {
.recipe {
display: block; /* turn off flexbox */
}
.recipe figure {
float: right;
width: 55%;
}
}

67. Demo: moving a photo on mobile
Flexbox enhanced Non-flexbox

68. Reordering on The Guardian
12 3
4 56
flex-direction: row-reverse
flex-direction: row-reverse
1
2
3
4
5
6

69. These examples don’t look wrong
or broken without flexbox.
Flexbox just enhances their sizing
and spacing to look better.

70. Step-by-step process for adding flexbox
to your UI components effectively
HOW
¨ 3.

71. Don’t freak out

72. Decide whether flexbox is the
right tool for the job

73. Decide which versions of
flexbox to support
standard, 2011/2012, and/or 2009

74. Browser support approaches to choose
¨ Use only the non-prefixed, standard syntax
¨ … plus browser-prefixed versions of
standard syntax
¨ … plus -ms- prefixed 2011/2012 syntax
¨ … plus -webkit- prefixed 2009 syntax
http://caniuse.com/#feat=flexbox

75. I recommend you skip the ‘09 syntax
¨ It’s slower to render than current syntax*
¨ Doesn’t support wrapping
¨ Its browsers have small market share
¨ If using flexbox for progressive
enhancement, its browsers can get same
fallback given to non-supporting browsers
* http://updates.html5rocks.com/2013/10/Flexbox-layout-isn-t-slow

76. Let tools add browser variants for you
Which variants do you want? Best tool to handle that
All the things! Autoprefixer
Bourbon (Sass)
Only the standard syntax,
with and without prefixes
Compass (Sass)
Some other combination
(such as everything except 2009)
Sass or LESS mixins, such as
https://github.com/mastastealth/
sass-flex-mixin

77. Add Modernizr as needed with flexbox
Flexbox and fallback styles can often co-
exist, but sometimes need to isolate them
http://zomigi.com/blog/using-modernizr-with-flexbox/

78. Or use @supports
.gallery-item {
display: inline-block;
}
@supports (flex-wrap: wrap) {
.gallery {
display: flex;
flex-wrap: wrap;
}
}
https://developer.mozilla.org/en-US/docs/Web/CSS/@supports
But IE 10-11, which do
support flexbox but
don’t support
@supports, won’t get
these styles

79. Choose and add appropriate
starter/fallback layout CSS

80. Things to consider
Do I need content blocks to wrap? not table-cell
Do I want to prevent blocks from wrapping? floats, inline-block, but
table-cell best
Do I need content-driven sizes? floats, but table-cell or
inline-block best
Do I need vertical alignment? inline-block, table-cell
Do I need horizontal alignment? floats, table-cell, inline-
block only with preset
sizes

81. Pick your starter layout CSS
¨ Floats
¨ table-cell
¨ inline-block
¨ Absolute positioning
Flexbox will override: Flexbox will not override:
Just use whatever you normally would;
flexbox plays nicely with most of them.

82. A real example of this process

83. Split left-right layout
Task: lay out review score
and price, on opposite
sides of same line
Needs:
¨ content-driven sizing
¨ horizontal alignment
¨ wrapping
score price or
“sold out”

84. Adding the starter CSS
.iw_mini_review_score_wrapper {
float: left;
}
.iw_mini_price_wrapper {
float: right;
}

85. Start adding flexbox!

86. Decide whether entire
component needs to be
block or inline-block
display:flex or inline-flex

87. Creating the block flex container
.iw_mini_details_wrapper {
display: flex;
}
.iw_mini_review_score_wrapper {
float: left;
}
.iw_mini_price_wrapper {
float: right;
}
Flex container sits
on a new row below,
like a block element

88. Decide flow of flex items

89. Things to consider
Lay out horizontally or vertically? flex-direction:row or
column
Allow boxes to wrap? flex-wrap:wrap,
wrap-reverse or nowrap
Order different than source? order values;
flex-direction:
row-reverse or
column-reverse

90. Allowing wrapping
.iw_mini_details_wrapper {
display: flex;
flex-wrap: wrap;
}
.iw_mini_review_score_wrapper {
float: left;
}
.iw_mini_price_wrapper {
float: right;
}
Allows second block to
wrap down if needed

91. Decide which items can
grow to fill space,
shrink to avoid overflow,
or must stay at a certain size

92. Tips for setting flex values
¨ Write out full flex values, rather than
using single-digit and keyword values
¤ flex: 1 1 0% instead of flex: 1
¤ Hidden default values can lead to mistakes
¤ Avoids IE 10-11 bugs
¨ Think about it backwards: first decide
flex-basis, then -shrink, then -grow

93. Tips for setting flex-basis values
¨ Acts like min-width when wrapping on
¨ If flex-wrap off and flex-shrink on,
browser can go smaller than flex-basis
¨ Be careful with flex-basis:0 when
wrapping
¨ Use flex-basis:auto whenever possible

94. Setting flex-shrink
¨ Always have at least 1 item per line that
can shrink (or wrap, or both)

95. Setting flex-grow
¨ Decide what to do with extra space
¤ Fill it up? (flex-grow: 1, 2, etc.)
¤ Leave it? (flex-grow: 0)

96. Setting flex values
.iw_mini_details_wrapper {
display: flex;
flex-wrap: wrap;
}
.iw_mini_review_score_wrapper {
float: left;
flex: 0 1 auto;
}
.iw_mini_price_wrapper {
float: right;
flex: 0 1 auto;
}
Size to content, shrink
smaller if you have to,
don’t grow bigger
(default value)

97. Decide how to align flex items

98. Main axis alignment
(horizontal when row,
vertical when column)
Cross axis alignment
(vertical when row,
horizontal when column)
(P.S. Also responsible for
equal-height columns)
justify-content align-items

99. Controlling alignment
.iw_mini_details_wrapper {
display: flex;
flex-wrap: wrap;
justify-content: space-between;
align-items: baseline;
}
.iw_mini_review_score_wrapper {
float: left;
}
.iw_mini_price_wrapper {
float: right;
}
Moves first item to left,
last item to right

100. Improved wrapping
Non-flexbox Flexbox enhanced

101. Flexbox with float fallback
.iw_mini_details_wrapper {
display: flex;
flex-wrap: wrap;
justify-content: space-between;
align-items: baseline;
}
.iw_mini_review_score_wrapper {
float: left;
}
.iw_mini_price_wrapper {
float: right;
}
Flexbox properties on
container override
floating automatically
in supporting browsers
Floating gets used by
old browsers

102. Test

103. Testing your flexbox
¨ Too Flexy bookmarklet for toggling
Modernizr flexbox classes:
http://chriswrightdesign.github.io/tooflexy/
¨ If reordering, check tabbing and screen
reading order to make sure it’s still logical

104. Fix bugs

105. Fixing browsers’ flexbox bugs
¨ Read explanations and workarounds by
Philip Walton:
https://github.com/philipwalton/flexbugs
¨ Let PostCSS fix some for you:
https://github.com/luisrudge/postcss-flexbugs-fixes

106. Summing up the process
1. Decide whether to use flexbox and which browser
versions of it
2. Choose and add starter layout CSS
3. Choose and add flexbox CSS
1. Block or inline-block container
2. Flow
3. Flex to control sizing
4. Alignment
4. Test and fix bugs

107. Flexbox is not for the future.
You can use flexbox today.

108. Thanks!
Zoe Mickley Gillenwater
@zomigi
design@zomigi.com
zomigi.com