COMP 135 Web Site Design Intermediate Week 7

CSS3 Layout Multicol Flexbox

Sane Layout Tools for CSS Stop using floats for layouts Intended use is to flow text around images Stop using positioning for layouts Achilles Heel of positioning was its disregard for other elements

Multi-Column Layout Allows content of element to be laid out in multiple columns Text can now flow from column to column Number of columns can vary depending on size of viewport t

Column Properties body {column-count: 2} /* body will contain two columns */ body {column-width: 16em} /* body will contain columns at least 16em wide, the number determined by available space */ body {columns: 2} body {columns: 16em} body {columns: 2 16em} /* this is legal though not practical */

Gaps and Rules body { column-gap: 2em; column-rule: thin solid black; } body { column-gap: 2em; column-rule-width: thin; column-rule-style: solid; column-rule-color: black; }

Fill and Span div { column-fill: balance; /* same length */ } h2 { column-span: all; /* h2 spans every column */ } h1 { break-before: column; break-inside: avoid-column; break-after: avoid-column; /* h1 have column breaks before them but inside and after the element breaks are to be avoided*/ }

Multi-Column Model Traditional CSS box model: Multi-column element: Content flows into content box of specified element Multi-column element: New container between content box and content: column box (columns) Content flows into column boxes of a multi-column element Column boxes arranged in rows have equal column width and equal column height Column boxes separated by column gaps and possible column rules Column rules only appear between column boxes with content in both Column boxes have no properties; cannot set backgrounds and have no concept of padding, margin or border

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Flexible Box Layout Module A.k.a the Flexible Box model or flexbox Contents of flex containers can be laid out in any flow direction (leftwards, rightwards, downwards or upwards) Display order can be reversed by CSS Laid out linearly along a single (main) axis or wrapped into multiple lines along a secondary (cross) axis Can “flex” their sizes to respond to available space Can align with the container or with respect to each other Can be collapsed along main axis and retain the container’s cross size

Flexbox Model Elements set with display: flex become flex containers Child elements are called flex items Flex layout is established along a flex flow direction

main axis main dimension The main axis of a flex container is the primary axis along which flex items are laid out. It extends in the main dimension. main-start main-end The flex items are placed within the container starting on the main-start side and going toward the main-end side. main size main size property A flex item's width or height, whichever is in the main dimension, is the item's main size. The flex item's main size property is either the ‘width’ or ‘height’ property, whichever is in the main dimension. cross axis cross dimension The axis perpendicular to the main axis is called the cross axis. It extends in the cross dimension. cross-start cross-end Flex lines are filled with items and placed into the container starting on the cross-start side of the flex container and going toward the cross-end side. cross size cross size property The width or height of a flex item, whichever is in the cross dimension, is the item's cross size. The cross size property is whichever of ‘width’ or ‘height’ that is in the cross dimension.

Flex Containers flex containers are not block containers flex and inline-flex set the display property of flex containers to be a block-level flex box container and inline-level flex box container, respectively flex containers are not block containers ‘column-’ properties of Multicol module have no effect ‘float’ and ‘clear’ have no effect ‘vertical-align’ has no effect

Flex Items Flex containers consist of zero or more flex items Child elements of flex container are flex items Each contiguous run of text in a flex container is contained in a flex item Flex item margins do not collapse visibility: collapse can be used to hide flex item without changing its cross size

Ordering and Orientation Flex Flow Direction Flex items can be laid out in any direction and in any order flex-direction row | row-reverse | column | column-reverse For row main axis has same orientation as in-line axis main-start and main-end equivalent to start and end row-reverse swaps main-start and main-end directions For column main axis has same orientation as block axis and main-start and main-end equivalent to before/head and after/foot directions, respectively column-reverse swaps main-start and main-end directions

Ordering and Orientation Flex Line Wrapping Flex containers can be single-line or multi-line Direction of cross-axis determines direction new lines are stacked in flex-wrap nowrap | wrap | wrap-reverse Flex containers are single-line with cross-start direction equivalent to either start or before/head direction whichever is the cross-axis and cross-end direction is the opposite direction to cross-start when value is nowrap wrap sets multi-line flex containers wrap-reverse same as wrap but swaps cross-start and cross- end directions

flex-flow flex-flow is the shorthand for setting flex-direction and flex-wrap properties div { flex-flow: row; } /* Initial value. Main-axis is inline, no wrap. */ div { flex-flow: column wrap; } /* Main-axis is block-direction (top to bottom) and lines wrap in the inline direction (rightwards). */ div { flex-flow: row-reverse wrap- reverse; } /* Main-axis is the opposite of inline direction (right to left). New lines wrap upward. */ 2 3 4 1 2 3 4 1 2 3 4 1

Ordering and Orientation Display Order Display order of flex items in flex container controlled by assignment to ordinal groups order <integer> Flex containers lay out flex items starting from lowest ordinal group going up Flex items in the same ordinal group laid out in the order they appear in the source document order should only be used for visual ordering and not logical or semantic ordering

The “Holy Grail Layout” <!DOCTYPE html> <header>...</header> <div id=“main”> <article>...</article> <nav>...</nav> <aside>...</aside> </div> <footer>...</footer> #main {display: flex;} #main>article {flex:1; order:2;} #main>nav {width:200px; order:1;} #main>aside {width:200px; order:3;} <header> <nav> <article> <aside> <footer>

Flexibility The “flex” Shorthand The defining property of a flex item alters the width or height of the flex item to fill available space Flex container distributes free space to flex items proportional to their flex grow factor and shrinks them to prevent overflow proportional to their flex shrink factor flex shorthand for flex-grow, flex-shrink, and flex- basis The flex-basis sets the initial main size of the flex item before free space is distributed If this value is omitted it is specified as a value of length zero It’s recommend to use the flex shorthand rather than the individual flex components

Diagram showing the difference between “absolute” flex (flex-basis: 0) and “relative” flex (flex-basis: auto) Initial value of flex is flex: 0 1 auto

Common Values of flex flex: 0 auto flex: initial flex: auto flex: none Equivalent to flex: 0 1 auto Sizes items based on width/height properties Items inflexible when free space is positive Allows items to shrink when space is insufficient flex: auto Equivalent to flex: 1 1 auto Makes items fully flexible Any free space left after items that are either flex:auto, flex:initial, or flex:auto have been size is assigned to the flex:auto items flex: none Equivalent to flex: 0 0 auto Sizes items based on width/height Items are inflexible and will not shrink flex: <positive-number> Equivalent to flex: <positive-number> 1 0px Makes item flexible

Alignment Alignment of flex items within the flex container is applied after flexing is finalized Can use margin: auto similar to how it is applied in box content The justify-content property aligns flex items along main axis of the current line of the flex container Applied after flexible lengths and auto margins are resolved Useful for distributing extra space when all items are inflexible

Alignment Cross-axis alignment achieved with align-items and align- self properties Flex items aligned along cross-axis similar to justify-content but in the perpendicular direction align-items sets default alignment for all flex items align-self allows default alignment to be overridden for individual flex items

Alignment For multi-line flex containers the align-content property can pack flex items along the cross-axis similar to the justify- content property aligns items within the main-axis

Old Flex and New Flex For the best browser support you may have to specify multiple prefix properties: display: -webkit-box; /* OLD - iOS 6-, Safari 3.1-6 */ display: -moz-box; /* OLD - Firefox 19- (buggy but mostly works) */ display: -ms-flexbox; /* TWEENER - IE 10 */ display: -webkit-flex; /* NEW - Chrome */ display: flex; /* NEW, Spec - Opera 12.1, Firefox 20+ */