Popoln vodnik po Flexboxu CSS-triki

Ozadje

Cilj Flexbox Layoutmodula (Prilagodljiva škatla) (priporočilo W3C za kandidate od oktobra 2017) je zagotoviti učinkovitejši način postavitve, poravnave in razporeditve prostora med predmeti v posodi, tudi če njihova velikost ni znana in / ali dinamična (torej beseda "flex").

Glavna ideja, ki stoji za prilagodljivo postavitvijo, je omogočiti vsebniku, da spremeni širino / višino (in vrstni red) svojih elementov, da najbolje zapolni razpoložljiv prostor (večinoma za prilagoditev vsem vrstam prikazovalnih naprav in velikostim zaslona). Prilagodljiv vsebnik razširi predmete, da zapolni prosti prostor ali pa jih zmanjša, da prepreči prelivanje.

Najpomembneje je, da je postavitev flexboxa usmerjena v nasprotju z običajnimi postavitvami (blok, ki je vertikalno in vrstica, ki je vodoravno). Čeprav se strani dobro obnesejo, jim primanjkuje prilagodljivosti (ni namenjena besedna igra) za podporo velikih ali zapletenih aplikacij (še posebej, ko gre za spreminjanje orientacije, spreminjanje velikosti, raztezanje, krčenje itd.).

Opomba: Postavitev Flexbox je najprimernejša za komponente aplikacije in manjše postavitve, medtem ko je postavitev mreže namenjena postavitvam večjega obsega.

Osnove in terminologija

Ker je flexbox cel modul in ne ena lastnost, vključuje veliko stvari, vključno s celotnim naborom lastnosti. Nekateri naj bi bili nastavljeni na vsebniku (nadrejeni element, znan kot "flex vsebnik"), drugi pa naj bi bili nastavljeni na podrejene elemente (omenjeni "flex elementi").

Če »običajna« postavitev temelji na blokovnih in vrstnih smereh pretoka, upogibna postavitev temelji na »smereh pretočnega pretoka«. Oglejte si to sliko v specifikaciji in razložite glavno idejo za prilagodljivo postavitev.

Elementi bodo razporejeni po main axis(od main-startdo main-end) ali navpični osi (od cross-startdo cross-end).

glavna os - glavna os fleksibilnega vsebnika je primarna os, vzdolž katere so postavljeni elementi fleks. Pazite, ni nujno vodoravno; odvisno od flex-directionlastnosti (glej spodaj).
glavni zagon | main-end - fleksibilni predmeti so nameščeni v vsebniku od glavnega začetka do glavnega konca.
glavna velikost - Širina ali višina upognjenega predmeta, ki je v glavni dimenziji, je glavna velikost predmeta. Lastnost glavne velikosti elementa flex je lastnost 'širina' ali 'višina', kar koli je v glavni dimenziji.
prečna os - os, pravokotna na glavno os, se imenuje prečna os. Njegova smer je odvisna od smeri glavne osi.
navzkrižni zagon | navzkrižni konec - upogibne črte se napolnijo s predmeti in vstavijo v posodo, začenši s strani navzkrižnega zagona upogljive posode in vodijo proti prečni strani.
velikost križa - širina ali višina upognjenega predmeta, kar koli je v prečni dimenziji, je križna velikost predmeta. Lastnost navzkrižne velikosti je ne glede na "širino" ali "višino", ki je v prečni dimenziji.

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Lastnosti nadrejenega
(fleks vsebnik)

zaslon

To definira fleks posodo; vrstica ali blok, odvisno od dane vrednosti. Omogoča prilagodljiv kontekst za vse svoje neposredne otroke.

.container ( display: flex; /* or inline-flex */ )

Upoštevajte, da stolpci CSS nimajo vpliva na flex vsebnik.

smer upogibanja

S tem se vzpostavi glavna os, s čimer se določi smer upogibnih elementov, ki so nameščeni v posodi za upogibanje. Flexbox je (razen neobveznega ovijanja) koncept postavitve v eno smer. Elemente flex predstavljajte predvsem kot vodoravne vrstice ali navpične stolpce.

.container ( flex-direction: row | row-reverse | column | column-reverse; )

row(privzeto): od leve proti desni v ltr; desno na levo vrtl
row-reverse: od desne proti levi v ltr; od leve proti desni vrtl
column: enako kot rowzgoraj navzdol
column-reverse: enako kot od row-reversespodaj navzgor

upogibanje

Privzeto se bodo vsi elementi flex skušali umestiti v eno vrstico. To lahko spremenite in dovolite, da se predmeti po potrebi povijajo s to lastnostjo.

.container ( flex-wrap: nowrap | wrap | wrap-reverse; )

nowrap (privzeto): vsi elementi flex bodo v eni vrstici
wrap: elementi flex bodo oviti v več vrstic, od zgoraj navzdol.
wrap-reverse: flex elementi se bodo previli v več vrstic od spodaj navzgor.

Tukaj je nekaj vizualnih predstavitev flex-wrap.

fleks-tok

To je okrajšava za lastnosti flex-directionin flex-wrap, ki skupaj določajo glavno in prečno os fleksibilnega vsebnika. Privzeta vrednost je row nowrap.

.container ( flex-flow: column wrap; )

upraviči vsebino

To določa poravnavo vzdolž glavne osi. Pomaga pri distribuciji dodatnega prostega prostora, ko so vsi elementi fleksibilnosti v vrstici neprilagodljivi ali prilagodljivi, vendar so dosegli največjo velikost. Prav tako ima določen nadzor nad poravnavo elementov, ko presežejo vrstico.

.container ( justify-content: flex-start | flex-end | center | space-between | space-around | space-evenly | start | end | left | right… + safe | unsafe; )

flex-start (privzeto): predmeti so zapakirani proti začetku upogibne smeri.
flex-end: predmeti so pakirani proti koncu upogibne smeri.
start: items are packed toward the start of the writing-mode direction.
end: items are packed toward the end of the writing-mode direction.
left: items are packed toward left edge of the container, unless that doesn’t make sense with the flex-direction, then it behaves like start.
right: items are packed toward right edge of the container, unless that doesn’t make sense with the flex-direction, then it behaves like end.
center: items are centered along the line
space-between: items are evenly distributed in the line; first item is on the start line, last item on the end line
space-around: items are evenly distributed in the line with equal space around them. Note that visually the spaces aren’t equal, since all the items have equal space on both sides. The first item will have one unit of space against the container edge, but two units of space between the next item because that next item has its own spacing that applies.
space-evenly: items are distributed so that the spacing between any two items (and the space to the edges) is equal.

Note that that browser support for these values is nuanced. For example, space-between never got support from some versions of Edge, and start/end/left/right aren’t in Chrome yet. MDN has detailed charts. The safest values are flex-start, flex-end, and center.

There are also two additional keywords you can pair with these values: safe and unsafe. Using safe ensures that however you do this type of positioning, you can’t push an element such that it renders off-screen (e.g. off the top) in such a way the content can’t be scrolled too (called “data loss”).

align-items

This defines the default behavior for how flex items are laid out along the cross axis on the current line. Think of it as the justify-content version for the cross-axis (perpendicular to the main-axis).

.container ( align-items: stretch | flex-start | flex-end | center | baseline | first baseline | last baseline | start | end | self-start | self-end +… safe | unsafe; )

stretch (default): stretch to fill the container (still respect min-width/max-width)
flex-start / start / self-start: items are placed at the start of the cross axis. The difference between these is subtle, and is about respecting the flex-direction rules or the writing-mode rules.
flex-end / end / self-end: items are placed at the end of the cross axis. The difference again is subtle and is about respecting flex-direction rules vs. writing-mode rules.
center: items are centered in the cross-axis
baseline: items are aligned such as their baselines align

The safe and unsafe modifier keywords can be used in conjunction with all the rest of these keywords (although note browser support), and deal with helping you prevent aligning elements such that the content becomes inaccessible.

align-content

This aligns a flex container’s lines within when there is extra space in the cross-axis, similar to how justify-content aligns individual items within the main-axis.

Note: This property only takes effect on multi-line flexible containers, where flex-flow is set to either wrap or wrap-reverse). A single-line flexible container (i.e. where flex-flow is set to its default value, no-wrap) will not reflect align-content.

.container ( align-content: flex-start | flex-end | center | space-between | space-around | space-evenly | stretch | start | end | baseline | first baseline | last baseline +… safe | unsafe; )

normal (default): items are packed in their default position as if no value was set.
flex-start / start: items packed to the start of the container. The (more supported) flex-start honors the flex-direction while start honors the writing-mode direction.
flex-end / end: items packed to the end of the container. The (more support) flex-end honors the flex-direction while end honors the writing-mode direction.
center: items centered in the container
space-between: items evenly distributed; the first line is at the start of the container while the last one is at the end
space-around: items evenly distributed with equal space around each line
space-evenly: items are evenly distributed with equal space around them
stretch: lines stretch to take up the remaining space

Properties for the Children
(flex items)

order

By default, flex items are laid out in the source order. However, the order property controls the order in which they appear in the flex container.

.item ( order: 5; /* default is 0 */ )

flex-grow

This defines the ability for a flex item to grow if necessary. It accepts a unitless value that serves as a proportion. It dictates what amount of the available space inside the flex container the item should take up.

If all items have flex-grow set to 1, the remaining space in the container will be distributed equally to all children. If one of the children has a value of 2, the remaining space would take up twice as much space as the others (or it will try to, at least).

.item ( flex-grow: 4; /* default 0 */ )

Negative numbers are invalid.

flex-shrink

This defines the ability for a flex item to shrink if necessary.

.item ( flex-shrink: 3; /* default 1 */ )

Negative numbers are invalid.

flex-basis

This defines the default size of an element before the remaining space is distributed. It can be a length (e.g. 20%, 5rem, etc.) or a keyword. The auto keyword means “look at my width or height property” (which was temporarily done by the main-size keyword until deprecated). The content keyword means “size it based on the item’s content” - this keyword isn’t well supported yet, so it’s hard to test and harder to know what its brethren max-content, min-content, and fit-content do.

.item ( flex-basis: | auto; /* default auto */ )

If set to 0, the extra space around content isn’t factored in. If set to auto, the extra space is distributed based on its flex-grow value. See this graphic.

flex

This is the shorthand for flex-grow, flex-shrink and flex-basis combined. The second and third parameters (flex-shrink and flex-basis) are optional. The default is 0 1 auto, but if you set it with a single number value, it’s like 1 0.

.item ( flex: none | ( ? || ) )

It is recommended that you use this shorthand property rather than set the individual properties. The shorthand sets the other values intelligently.

align-self

This allows the default alignment (or the one specified by align-items) to be overridden for individual flex items.

Please see the align-items explanation to understand the available values.

.item ( align-self: auto | flex-start | flex-end | center | baseline | stretch; )

Note that float, clear and vertical-align have no effect on a flex item.

Examples

Let’s start with a very very simple example, solving an almost daily problem: perfect centering. It couldn’t be any simpler if you use flexbox.

.parent ( display: flex; height: 300px; /* Or whatever */ ) .child ( width: 100px; /* Or whatever */ height: 100px; /* Or whatever */ margin: auto; /* Magic! */ )

This relies on the fact a margin set to auto in a flex container absorb extra space. So setting a vertical margin of auto will make the item perfectly centered in both axes.

Now let’s use some more properties. Consider a list of 6 items, all with fixed dimensions, but can be auto-sized. We want them to be evenly distributed on the horizontal axis so that when we resize the browser, everything scales nicely, and without media queries.

.flex-container ( /* We first create a flex layout context */ display: flex; /* Then we define the flow direction and if we allow the items to wrap * Remember this is the same as: * flex-direction: row; * flex-wrap: wrap; */ flex-flow: row wrap; /* Then we define how is distributed the remaining space */ justify-content: space-around; )

Done. Everything else is just some styling concern. Below is a pen featuring this example. Be sure to go to CodePen and try resizing your windows to see what happens.

Let’s try something else. Imagine we have a right-aligned navigation element on the very top of our website, but we want it to be centered on medium-sized screens and single-columned on small devices. Easy enough.

/* Large */ .navigation ( display: flex; flex-flow: row wrap; /* This aligns items to the end line on main-axis */ justify-content: flex-end; ) /* Medium screens */ @media all and (max-width: 800px) ( .navigation ( /* When on medium sized screens, we center it by evenly distributing empty space around items */ justify-content: space-around; ) ) /* Small screens */ @media all and (max-width: 500px) ( .navigation ( /* On small screens, we are no longer using row direction but column */ flex-direction: column; ) )

Let’s try something even better by playing with flex items flexibility! What about a mobile-first 3-columns layout with full-width header and footer. And independent from source order.

.wrapper ( display: flex; flex-flow: row wrap; ) /* We tell all items to be 100% width, via flex-basis */ .wrapper> * ( flex: 1 100%; ) /* We rely on source order for mobile-first approach * in this case: * 1. header * 2. article * 3. aside 1 * 4. aside 2 * 5. footer */ /* Medium screens */ @media all and (min-width: 600px) ( /* We tell both sidebars to share a row */ .aside ( flex: 1 auto; ) ) /* Large screens */ @media all and (min-width: 800px) ( /* We invert order of first sidebar and main * And tell the main element to take twice as much width as the other two sidebars */ .main ( flex: 2 0px; ) .aside-1 ( order: 1; ) .main ( order: 2; ) .aside-2 ( order: 3; ) .footer ( order: 4; ) )

Prefixing Flexbox

Flexbox requires some vendor prefixing to support the most browsers possible. It doesn’t just include prepending properties with the vendor prefix, but there are actually entirely different property and value names. This is because the Flexbox spec has changed over time, creating an “old”, “tweener”, and “new” versions.

Perhaps the best way to handle this is to write in the new (and final) syntax and run your CSS through Autoprefixer, which handles the fallbacks very well.

Alternatively, here’s a Sass @mixin to help with some of the prefixing, which also gives you an idea of what kind of things need to be done:

@mixin flexbox() ( display: -webkit-box; display: -moz-box; display: -ms-flexbox; display: -webkit-flex; display: flex; ) @mixin flex($values) ( -webkit-box-flex: $values; -moz-box-flex: $values; -webkit-flex: $values; -ms-flex: $values; flex: $values; ) @mixin order($val) ( -webkit-box-ordinal-group: $val; -moz-box-ordinal-group: $val; -ms-flex-order: $val; -webkit-order: $val; order: $val; ) .wrapper ( @include flexbox(); ) .item ( @include flex(1 200px); @include order(2); )

Related Properties

A Complete Guide to Grid
Almanac entries on Grid properties, like grid-row / grid-column

Other Resources

Flexbox in the CSS specifications
Flexbox at MDN
Flexbox at Opera
Diving into Flexbox by Bocoup
Mixing syntaxes for best browser support on CSS-Tricks
Flexbox by Raphael Goetter (FR)
Flexplorer by Bennett Feely

Bugs

Flexbox is certainly not without its bugs. The best collection of them I’ve seen is Philip Walton and Greg Whitworth’s Flexbugs. It’s an open-source place to track all of them, so I think it’s best to just link to that.

Podpora za brskalnik

Razčlenjeno po "različici" flexboxa:

(novo) pomeni nedavno sintakso iz specifikacije (npr. display: flex;)
(tweener) pomeni nenavadno neuradno skladnjo iz leta 2011 (npr. display: flexbox;)
(staro) pomeni staro skladnjo iz leta 2009 (npr. display: box;)

Chrome	Safari	Firefox	Opera	IE	Rob	Android	iOS
20- (staro) 21+ (novo)	3,1+ (staro) 6,1+ (novo)	2–21 (stari) 22+ (novi)	12,1+ (novo)	10 (tweener) 11+ (novo)	17+ (novo)	2,1+ (staro) 4,4+ (novo)	3,2+ (staro) 7,1+ (novo)

Brskalnik Blackberry 10+ podpira novo sintakso.