ca 272 - professional web site development css positioning

CA 272 - Professional Web Site Development

CSS Positioning

Announcements

CA/CS Advising Day in Faculty Dining Room: Wed., 11/28 from 3:00 to 6:30 p.m.

I am speaking with Prof. Lizmi’s ColdFusion class about the Web design/development business: Wed., 11/28 at 6:00 p.m., HU 313

Review - Positioning Schemes

1. Static - a.k.a. ‘normal flow’

2. Relative - offset by some value

3. Absolute - positioned at specified coordinates outside normal flow

4. Fixed - positioned to viewport

5. (Float - displaces text only)

Static Positioning

Normal flow - not ‘positioned’ Block-level elements generate an (invisible)

box Elements ‘flow’ one after another; elements

are displaced by previous elements in code Elements cannot appear side by side One-column layout

Relative Positioning

Element is offset by some value (relative to original position)

Element retains shape it would have had in normal flow

Normal flow preserves space originally taken up by element

Element may overlap other elements Good for establishing positioning context

Relative Positioning

Example: relative positioned div Exercise: relative positioned span

Open blank HTML document Insert a few paragraphs of text Wrap (CTRL-T) some text in <span

class=“example”>…</span> Create style rule for span with positioning type

‘relative’ and some offset values

Absolute Positioning

Element is completely removed from normal flow (and space it occupied disappears)

Placement is specified by offset values (relative to containing block)

Always generates block-level box Absolutely positioned elements do not interact with

each other (except for stacking order) Must know exact coordinates to position elements See example

Fixed Positioning

Just like Absolute Positioning, except… Elements positioned relative to viewport

(browser window) - scrolling window does not affect element

Good for frame-like layouts IE 6 and under do not support fixed

positioning See example

Floats

(Not actually a positioning scheme - elements can be floated AND positioned)

Elements removed from normal flow… EXCEPT floated elements displace text in normal

flow (but NOTHING ELSE) Floated elements displace other floated elements! Margins on floats do not collapse Use clear: left | right | both; on OTHER elements to

keep them from being beside a floated element

Positioning Context - the Containing Block

Containing block determines where positioned element is placed

For static and relative positioning, containing block is nearest block-level, table cell or inline box parent

Positioning Context (continued)

For absolute positioning, containing block is nearest positioned element (relative, absolute or fixed)

Default positioning context is <body> element (document window)

For fixed positioning, containing block is viewport

Offset Values Top, Bottom, Right, Left Units: length (px) or percentage (%) Offset values are relative to containing

block Positive values move element inward

(relative to containing block) Negative values move element

outwards % values are relative to height and width of containing

block Should give top or bottom AND side value Default is top: 0; left: 0;

Stacking Order: z-index

Elements can be positioned 3-dimensionally along the z axis using z-index (only ‘positioned’ elements)

Higher values of z-index are further on top

z-index can be negative Normal flow elements are

z-index: 0; Local stacking context

Other Layout Properties

Width/Height - important for constraining size of layout elements >> Floated elements MUST have width specified

Display: block; - when we want inline element to behave as block element (e.g., anchor as button)

Overflow: visible | hidden | scroll Max-width/max-height & min-width/min-height

>> very useful for liquid layouts Unsupported by older versions of IE

Exercise: Absolute Positioning

Open a blank HTML document in DW Go to the Layout tab in the Insert Bar

Draw some boxes in Design View (these will be absolutely positioned divs)

Go to Code View and view the CSS position: absolute; left; top; width; height; z-

index

Exercise: Absolute Positioning (continued)

Click on one of your divs and add some text; make text a paragraph

Click on AP div ‘handle’ to select it Delete height value in Property Inspector You can change left, top, width, height (also

drag with handle and bounding box)


Set background color on divs Drag one div to overlap another Change z-index values (set lowest one to

highest value) Select overlapping div and Edit > Cut Click in other div and Edit > Paste Why is div in different place?


Insert several paragraphs of text in an AP div (e.g., from lipsum.com)

Select div and set height (to value smaller than height of text) - view change

Set overflow to hidden - view change Set overflow to scroll; preview in browser

Web Layout Patterns

Common elements in Web layouts: Branding & Marketing Navigation (main nav, page nav, etc.) Primary content (often text content) Supplemental content (sidebars, calls to action,

ads, images, etc.) Footer content and site tools

Review: Page Layout Schemes

Fixed width - width set to fixed px value Most designers use fixed width because easiest

to design for PRO: easier to design graphics for, can set

readable line lengths of text CON: doesn’t take advantage of screen width for

users with large monitors; users with smaller monitors may have to scroll horizontally

Page Layout Dimensions

Fixed design for pixel widths - must account for browser ‘chrome’, scrollbars

800 x 600 monitor: 750px (or 760px) width Safest width, but only 12% of users

1024 x 800 monitor: 950px+ width Most users have this resolution now (53%)

1280 x 1024 is gaining (~23%) Don’t worry about 640 x 480 anymore

Page Layout Schemes

Fluid/Liquid - width set to % value, adjusts to width of browser window PRO: makes full use of browser window; user can

resize CON: may lead to very long lines of text; harder to

design for See: http://www.drexel.edu/

Page Layout Schemes

Elastic - width set in relative units (ems) Page elements grow proportionately as user

resizes text size PRO: ideal for accessibility - users can view at

whatever scale is comfortable for them CON: very difficult to code; can lead to very large

widths as user increases font size Rarely used

Web Layouts

Examples: www.starbucks.com www.hueylong.com www.newyorker.com www.gohawaii.com www.craigslist.org

Web Layout Patterns

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CSS Layouts with Floats and Positioning

Review: two-column float with clearing footer

Wrapper encloses everything

Each column is floated

Footer clears floats and extends wrapper

Column backgrounds are on #wrapper

CSS Layouts with Absolute Positioning

Can replicate layout with AP divs

BUT, must know placement of alldivs

How do you place footer if variable content?

How do you create column backgrounds for unknown height?

CSS Layouts with AP - continued

Absolute positioning is useful for positioning elements WITHIN layouts

E.g., masthead graphics See “liquid layout” (linked on class

homepage)

CSS Image Replacement

What if we want to replace text with a graphic? (using CSS only)

Should leave text in HTML for accessibility and SEO Many techniques; most common (probably) is

‘Phark’ method: text-indent: -5000px; e.g. h1#logo {

text-indent: -5000px; background: url(logo.gif) 0 0 no-repeat; width and height as needed}

Coca-Cola

CSS Image Replacement

Downsides: If images are turned off (but CSS is on) nothing

will display Background images usually do not print If you edit text, you’ll need to edit the graphic

Exercise: Image Replacement

Download from the class site: Float layout (save to homework folder) Nav button background image (save to images

folder) Join button jpeg (save to images folder)

Insert a link, “Join Today!”, at the beginning of the second paragraph of simple-page-layout4a.html

Give this link class ‘joinButton’

Exercise: Image Replacement (continued)

Create CSS styles (for default state and :hover) to make link a button with join.jpg as background image (button should be 100px by 100px)(display; width; height; background; etc.)

Float button right and add left and bottom margins Preview in browser Need to hide text of link:

text-indent: -5000px; Preview in Firefox - click and hold down button

should see dotted box off to left Add outline: none; and preview again

Homework

Rework homework 16 to float both left and right columns, using wrapper div and clearing footer

Create a third column inside div#rtCol Read Chapters 8 & 14 in the Visual

QuickStart Guide

ca 272 - professional web site development css positioning

Documents

relative positioning

positioned elements

element element

relative positioning

absolute positioning

positioning context

positioning scheme elements

fixed positioning