Post on 14-Mar-2020
Cascading Style Sheets (CSS)
CSI 3140WWW Structures, Techniques and Standards
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Motivation
wHTML markup can be used to representn Semantics: h1 means that an element is a top-level
headingn Presentation: h1 elements look a certain way
wIt’s advisable to separate semantics from presentation because:
n It’s easier to present documents on multiple platforms(browser, cell phone, spoken, …)
n It’s easier to generate documents with consistent lookn Semantic and presentation changes can be made
independently of one another (division of labor)n User control of presentation is facilitated
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Style Sheet Languages
wCascading Style Sheets (CSS)n Applies to (X)HTML as well as XML documents
in generaln Focus of this chapter
wExtensible Stylesheet Language (XSL)n Often used to transform one XML document to
another form, but can also add stylen XSL Transformations covered in later chapter
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
wA styled HTML document
produced by the style sheet style1.css:
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
link element associates style sheet with doc.
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
type attribute specifies style language used
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
href attribute provides style sheet URL
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
title attribute provides style sheet name
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
Alternative, user selectable style sheetscan be specified
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
wA styled HTML document
produced by the style sheet style2.css:
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
Note that alternate, user selectable style is not widely supported: firefox 3 and IE 8 do, but IE 6, IE 7 and Chrome don’t.
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Introduction
wSingle document can be displayed on multiple media platforms by tailoring style sheets:
This document will be printed differently than it is displayed.
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax
wParts of a style rule (or statement)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wSingle element type:
wMultiple element types:
wAll element types:
wSpecific elements by id:
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wElements belonging to a style class:
n Referencing a style class in HTML:
wElements of a certain type and class:
class selector: begins with a period .
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wElements belonging to a style class:
n Referencing a style class in HTML:
wElements of a certain type and class:this span belongs to three style classes
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wElements belonging to a style class:
n Referencing a style class in HTML:
wElements of a certain type and class:
this rule applies only to span’s belonging to class special
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wSource anchor elements:
wElement types that are descendents:pseudo-classes
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wSource anchor elements:
wElement types that are descendants:
rule applies to li element that is
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wSource anchor elements:
wElement types that are descendants:
rule applies to li element that ispart of the content of an ol element
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax:Selector Strings
wSource anchor elements:
wElement types that are descendants:
rule applies to li element that ispart of the content of an ol elementthat is part of the content of a ul element
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Syntax
wStyle rules covered thus far follow ruleset syntaxwAt-rule is a second type of rule
n Reads style rules from specified URLn Must appear at beginning of style sheet
URL relative to style sheet URL
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Style Sheets and HTML
wStyle sheets referenced by link HTML element are called external style sheetswStyle sheets can be embedded directly in HTML document using style element
wMost HTML elements have style attribute (value is list of style declarations)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Style Sheets and HTML
wRules of thumb:n Use external style sheets to define site-wide stylen Prefer style sheets (either external or embedded)
to style attributesn XML special characters
l Must use references in embedded style sheets and style attribute
l Must not use references in external style sheets
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Rule Cascade
wWhat if more than one style declaration applies to a property of an element?
wThe CSS rule cascade determines which style rule’s declaration applies
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Rule Cascade
To find the value for an element/property combination, user agents must apply the following sorting order:
1- Find all declarations that apply to the element and property in question, for the target media type. Declarations apply if the associated selector matches the element in question.
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Rule Cascade
2- The primary sort of the declarations is by weight and origin: for normal declarations, author style sheets override user style sheets which override the default style sheet. For "!important" declarations, user style sheets override author style sheets which override the default style sheet. "!important" declaration override normal declarations. An imported style sheet has the same origin as the style sheet that imported it.
Five origin/weight levels:1. user/important2. author/important3. author/normal4. user/normal5. user agent/normal
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Rule Cascade
3- The secondary sort is by specificity of selector: more specific selectors will override more general ones. Pseudo-elements and pseudo-classes are counted as normal elements and classes, respectively.
Specificity:1. style attribute2. rule with selector:
1. ID2. class/pseudo-class3. descendant/element type4. universal
3. HTML attribute
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Rule Cascade
4- Finally, sort by order specified: if two rules have the same weight, origin and specificity, the latter specified wins. Rules in imported style sheets are considered to be before any rules in the style sheet itself.
Conceptually, create onelong style sheet. Laterstyle rules have higherpriority than earlier rules.
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Inheritance
wWhat if no style declaration applies to a property of an element?wGenerally, the property value is inherited from the nearest ancestor element that has a value for the propertywIf no ancestor has a value (or the property does not inherit) then CSS defines an initial value that is used
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Inheritance
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Inheritance
wProperty values:n Specified: value contained in declaration
l Absolute: value can be determined without reference to context (e.g., 2cm)
l Relative: value depends on context (e.g., larger)n Computed: absolute representation of relative
value (e.g., larger might be 1.2 x parent font size)
n Actual: value actually used by browser (e.g., computed value might be rounded)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Inheritance
wMost properties inherit computed valuen Exception discussed later: line-height
wA little thought can usually tell you whether a property inherits or not
n Example: height does not inherit
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
Glyph (visual representation)
character cell(content area)
wA font is a mapping from code points to glyphs
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wA font is a mapping from code points to glyphs
glyphs do not necessary stay inside cells!
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wA font family is a collection of related fonts (typically differ in size, weight, etc.)
wfont-family property can accept a list of families, including generic font families
first choice font
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wA font family is a collection of related fonts (typically differ in size, weight, etc.)
wfont-family property can accept a list of families, including generic font families
second choice font
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wA font family is a collection of related fonts (typically differ in size, weight, etc.)
wfont-family property can accept a list of families, including generic font families
generic
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
genericfonts aresystem-specific
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wNote that most generic font can be easily set on Firefox and Chrome, but such option doesn’t seem to be available on IE 7 and 8. IE will still default to something although maybe not what you had hoped for!
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wMany properties, such as font-size, have a value that is a CSS lengthwAll CSS length values except 0 need units
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
Computed valueof font-sizeproperty
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wReference font defines em and ex unitsn Normally, reference font is the font of the
element being styledn Exception: Using em/ex to specify value for font-size
parent element’s font isreference font
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wOther ways to specify value for font-size:
n Percentage (of parent font-size)
n Absolute size keyword: xx-small, x-small, small, medium (initial value), large, x-large, xx-largel User agent specific; should differ by ~ 20%
n Relative size keyword: smaller, largerl Relative to parent element’s font
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wText is rendered using line boxes
wHeight of line box given by line-heightn Initial value: normal (i.e., cell height; relationship with
em height is font-specific)n Other values (following are equivalent):
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wWhen line-height is greater than cell height:
wInheritance of line-height:n Specified value if normal or unit-less numbern Computed value otherwise
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wfont shortcut property:
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wfont shortcut property:
Initial values used if no value specified in fontproperty list (that is, potentially reset)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Font Properties
wfont shortcut property:
specifying line-height (here, twice cell height)
any order size and family required,order-dependent
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Text Formatting
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Text Color
wFont color specified by color propertywTwo primary ways of specifying colors:
n Color name: black, gray, silver, white, red, lime, blue, yellow, aqua, fuchsia, maroon, green, navy, olive, teal, purple, full list athttp://www.w3.org/TR/SVG11/types.html#ColorKeywords
n red/green/blue (RGB) values
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Text Color
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Text Color
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
wEvery rendered element occupies a box:
(or inner edge)
(or outer edge)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Box Model
wIf multiple declarations apply to a property, the last declaration overrides earlier specifications
Left border is 30px wide, inset style, and red
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Backgrounds
wbackground-colorn Specifies background color for content, padding,
and border areasn Margin area is always transparentn Not inherited; initial value transparent
wbackground-imagen Specifies (using url() function) image that
will be tiled over an element
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Backgrounds
<body style="background-image:url('CucumberFlowerPot.png')">
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wIn normal flow processing, each displayed element has a corresponding box
n html element box is called initial containing block and corresponds to entire document
n Boxes of child elements are contained in boxes of parent
n Sibling block elements are laid out one on top of the other
n Sibling inline elements are one after the other
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout(body)
(html)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
Blockelementsonly
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layouthtml
bodydiv d1div d2div d3
div d4
Top edges ofblock boxes arein document order
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wWhat is a “block element”?n Element with value block specified for its display property
n User agent style sheet (not CSS) specifies default values; typical block elements include html, body, p, pre, div, form, ol, ul, dl, hr, h1through h6
n Most other elements except li and table-related have inline specified for display
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wWhen blocks stack, adjacent margins are collapsed to the size of the larger margin
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wInitial value of width property is auto, which for block boxes means to make the content area as wide as possible within margin/padding constraints:
Width of block boxesincreases as browserclient area is widened
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wCan also specify CSS length or percentage (of parent’s content width) for widthproperty
By default, width of right margin is adjusted to accommodate a change to width
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wCan also specify CSS length or percentage (of parent’s content width) for widthproperty
Centering can be achieved by settingboth margins to auto
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wBoxes corresponding to character cells and inline elements are laid out side by side in line boxes that are stacked one on top of the other
Character cells aligned by baseline
Heights based oncontent
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
Padding/borders/margins affect width but not height of inline boxes
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Normal Flow Layout
wSpecify value for vertical-align to position an inline element within line box:
initial value of vertical-align
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wCSS allows for boxes to be positioned outside the normal flow:
n Relative positioning
span’s shifted backwards relative to normal flow
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wCSS allows for boxes to be positioned outside the normal flow:
n Float positioning
span taken out of normalflow and “floated” to theleft of its line box
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wCSS allows for boxes to be positioned outside the normal flow:
n Absolute positioning
span’s removed fromnormal flow andpositioned relativeto another box
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wProperties used to specify positioning:n position: static (initial value), relative, or absolutel Element is positioned if this property not staticl Properties left, right, top, bottom apply to
positioned elementsw Primary values are auto (initial value) or CSS length
n float: none, left, or rightl Applies to elements with static and relative
positioning only
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wRelative positioningn Specifying positive value for right property of
relatively positioned box moves it to left
<span style="background-color:red"> </span><span class="right">Red</span>
spancontainingtext movesleft
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wRelative positioningn Specifying negative value for left property
also moves box to left
<span style="background-color:red"> </span><span class="right">Red</span>
sameeffect asbefore
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wFloat positioningn Specify value for float property
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wFloat positioningn Specify value for float property
Floated element becomes a CSS blockelement (e.g., can set height and width)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wAbsolute positioningn Specify location for corner of box relative to
positioned containing block
margin areapadding area
containingblock
This second paragraph has anote.
p elements are positioned (but don’t move!)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wAbsolute positioningn Specify location for edges of box relative to
positioned containing block
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wAbsolute positioning10em padding top
edge
padding leftedge
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wAbsolute positioning
8em
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
Beyond Normal Flow
wAbsolutely positioned box does not affect positioning of other boxes!
Second absolutelypositioned boxobscures first
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Position-Related Properties
wz-index: drawing order for overlaid boxes (largest number drawn last)
Guy-Vincent Jourdan :: CSI 3140 :: based on Jeffrey C. Jackson’s slides
CSS Position-Related Properties
wdisplay: value none means that element and its descendants are not rendered and do not affect normal flowwvisibility: value hidden (initial value is visible) means that element and its descendants are not rendered but still do affect normal flow