CSSE 290 Web Programming

Lecture 4: CSS properties and Selectors

Reading: 3.2 - 4.1;

Except where otherwise noted, the contents of this document are Copyright 2012 Marty Stepp, Jessica Miller, and Victoria Kirst. All rights reserved. Any redistribution, reproduction, transmission, or storage of part or all of the contents in any form is prohibited without the author's expressed written permission.

Otherwise note: Claude Anderson was given permission to modify the slides for CSSE 290 at Rose-Hulman by author Jessica Miller. The authors' original slides, based on Web Programming Step by Step, can be seen at http://webstepbook.com.

Some of the examples in some days' slides are from David Fisher at Rose-Hulman, who was kind enough to allow me to use them. My intention is to mark these examples with [DSF].

HTML tables: <table>, <tr>, <td>

A 2D table of rows and columns of data (block element)

<table>
	<tr><td>1,1</td><td>1,2 okay</td></tr>
	<tr><td>2,1 real wide</td><td>2,2</td></tr>
</table>

• table defines the overall table, tr each row, and td each cell's data
• tables are useful for displaying large row/column data sets
• NOTE: tables are sometimes used by novices for web page layout, but this is not proper semantic HTML and should be avoided

Table headers, captions: <th>, <caption>

<table>
	<caption>My important data</caption>
	<tr><th>Column 1</th><th>Column 2</th></tr>
	<tr><td>1,1</td><td>1,2 okay</td></tr>
	<tr><td>2,1 real wide</td><td>2,2</td></tr>
</table>

• th cells are considered headers; by default, they appear bold
• a caption before the table indicates its purpose

CSS properties for text

property	description
text-align	alignment of text within its element
text-decoration	decorations such as underlining
text-indent	indents the first letter of each paragraph
text-shadow	a colored shadow near an existing piece of text
line-height, word-spacing, letter-spacing	gaps between the various portions of the text
Complete list of text properties

Details on the next few slides

text-align

blockquote { text-align: justify; }
h2 { text-align: center; }

• can be left, right, center, or justify (which widens all full lines of the element so that they occupy its entire width)

text-decoration

p {
	text-decoration: underline;
}

• can also be overline, line-through, blink, or none
• effects can be combined:

  text-decoration: overline underline;

text-shadow

p {
	font-weight: bold;
	text-shadow: -2px 5px gray;
}

• shadow is specified as an X-offset, a Y-offset, and an optional color

The list-style-type property

ol { list-style-type: lower-roman; }

• Possible values:
  1. none : No marker
  2. disc (default), circle, square
  3. decimal : 1, 2, 3, etc.
  4. decimal-leading-zero : 01, 02, 03, etc.
  5. lower-roman : i, ii, iii, iv, v, etc.
  6. upper-roman : I, II, III, IV, V, etc.
  7. lower-alpha : a, b, c, d, e, etc.
  8. upper-alpha : A, B, C, D, E, etc.
  9. lower-greek : alpha, beta, gamma, etc.
  10. others: hebrew, armenian, georgian, cjk-ideographic, hiragana, katakana, hiragana-iroha, katakana-iroha

CSS properties for backgrounds

background-image

body {
	background-image: url("images/draft.jpg");
}

• background image/color fills the element's content area

background-repeat

body {
	background-image: url("images/draft.jpg");
	background-repeat: repeat-x;
}

• can be repeat (default), repeat-x, repeat-y, or no-repeat

background-position

body {
	background-image: url("images/draft.jpg");
	background-repeat: no-repeat;
	background-position: 370px 20px;
}

• value consists of two tokens, each of which can be top, left, right, bottom, center, a percentage, or a length value in px, pt, etc.
• value can be negative to shift left/up by a given amount

Body styles

body {
	font-size: 16px;
}

• to apply a style to the entire body of your page, write a selector for the body element
• saves you from manually applying a style to each element

Styles that conflict

body { color: green; }
p, h1, h2 { color: blue; font-style: italic; }
h2 { color: red; background-color: yellow; }

• when two identical selectors set conflicting values for the same property, the latter style takes precedence
• (later we will learn about more specific styles that can override more general styles)

Embedding style sheets: <style> (BAD!)

<head>
	<style type="text/css">
		p { font-family: sans-serif; color: red; }
		h2 { background-color: yellow; }
	</style>
</head>

• CSS code can be embedded within the head of an HTML page
• this is bad style; DO NOT DO THIS (why?)

Inline styles: the style attribute (BAD!)

<p style="font-family: sans-serif; color: red;">
This is a paragraph</p>

• higher precedence than embedded or linked styles
• used for one-time overrides and styling a particular element
• this is bad style; DO NOT DO THIS (why?)

Content vs. presentation

• HTML is for content; what is on the page (heading; list; code; etc.)
• CSS is for presentation; how to display the page (bold; centered; 20px margin; etc.)
• keeping content separate from presentation is a very important web design principle
• If the HTML contains no styles, its entire appearance can be changed by swapping .css files
• see also: CSS Zen Garden

Cascading style sheets

• it's called Cascading Style Sheets because the properties of an element cascade together in this order:
  • browser's default styles (reference)
  • external style sheet files (in a <link> tag)
  • internal style sheets (in a <style> tag in the page header)
  • inline style (the style attribute of an HTML element)

Inheriting styles

body { font-family: sans-serif; background-color: yellow; }
p { color: red; background-color: aqua; }
a { text-decoration: overline underline; }
h2 { font-weight: bold; text-align: center; }

• when multiple styles apply to an element, they are inherited
• a more tightly matching selection rule can override a more general inherited rule
• not all properties are inherited (notice link's color above)

CSS pseudo-classes

a:link    { color: #FF0000; }      /* unvisited link */
a:visited { color: #00FF00; }      /* visited link */
a:hover   { color: #FF00FF; }      /* mouse over link */

There are several other pseudo-classes. Follow the link in the slide title.

Motivation for page sections

• want to be able to style individual elements, groups of elements, sections of text or of the page
• (later) want to create complex page layouts

The HTML id attribute

<p>Spatula City!  Spatula City!</p>
<p id="mission">Our mission is to provide the most
spectacular spatulas and splurge on our specials until our
customers <q>esplode</q> with splendor!</p>

• allows you to give a unique ID to any element on a page
• each ID can only be used once in the page

Linking to sections of a web page

<p>Visit <a href=
		"http://www.textpad.com/download/index.html#downloads">
	textpad.com</a> to get the TextPad editor.</p>

<p><a href="#mission">View our Mission Statement</a></p>

• a link target can include an ID at the end, preceded by a #
• browser will load that page and scroll to element with given ID

CSS ID selectors

#mission {
	font-style: italic;
	font-family: "Garamond", "Century Gothic", serif;
}

• applies style only to the HTML element that has the ID of mission
• element can be specified explicitly: p#mission {

The HTML class attribute

<p class="shout">Spatula City!  Spatula City!</p>
<p class="special">See our spectacular spatula specials!</p>
<p class="special">Today only: satisfaction guaranteed.</p>

• classes are a way to group some elements and give a style to only that group
  (I don't want ALL paragraphs to be yellow, just these three...)
• unlike an id, a class can be reused as many times as you wish on a page

CSS class selectors

.special {                   /* any element with class="special" */
	background-color: yellow;
	font-weight: bold;
}
p.shout {                    /* only p elements with class="shout" */
	color: red;
	font-family: cursive;
}

• applies rule to any element with class special, or a p with class shout

Multiple classes

<h2 class="shout">Spatula City!  Spatula City!</h2>
<p class="special">See our spectacular spatula specials!</p>
<p class="special shout">Satisfaction guaranteed.</p>
<p class="shout">We'll beat any advertised price!</p>

• an element can be a member of multiple classes (separated by spaces)

CSS for following examples

.special {
	background-color: yellow;
	font-weight: bold;
}
.shout {
	color: red;
	font-family: cursive;
}

• for the next several slides, assume that the above CSS rules are defined

Sections of a page: <div>

a section or division of your HTML page (block)

<div class="shout">
	<h2>Spatula City!  Spatula City!</h2>
	<p class="special">See our spectacular spatula specials!</p>
	<p>We'll beat any advertised price!</p>
</div>

• a tag used to indicate a logical section or area of a page
• has no appearance by default, but you can apply styles to it

Inline sections: <span>

an inline element used purely as a range for applying styles

<h2>Spatula City!  Spatula City!</h2>
<p>See our <span class="special">spectacular</span> spatula specials!</p>
<p>We'll beat <span class="shout">any advertised price</span>!</p>

• has no onscreen appearance, but you can apply a style or ID to it, which will be applied to the text inside the span

Recap: CSS context selectors

selector1 selector2 {
	properties
}

• applies the given properties to selector2 only if it is inside a selector1 on the page

selector1 > selector2 {
	properties
}

• applies the given properties to selector2 only if it is directly inside a selector1 on the page (selector2 tag is immediately inside selector1 with no tags in between)

Context selector example

<p>Shop at <strong>Hardwick's Hardware</strong>...</p>
<ul>
	<li>The <strong>best</strong> prices in town!</li>
	<li>Act while supplies last!</li>
</ul>

li strong { text-decoration: underline; }

More complex example

<div id="ad">
	<p>Shop at <strong>Hardwick's Hardware</strong>...</p>
	<ul>
		<li class="important">The <strong>best</strong> prices!</li>
		<li>Act <strong>while supplies last!</strong></li>
	</ul>
</div>

#ad li.important strong { text-decoration: underline; }

Exercises

• follow the link from the schedule page to get and unpack today's exercise folder
• Read the Instructions.html file
• Do Exercises Part 1

The CSS Box Model

• for layout purposes, every element is composed of:
  • the actual element's content
  • a border around the element
  • padding between the content and the border (inside)
  • a margin between the border and other content (outside)
• width = content width + L/R padding + L/R border + L/R margin
  height = content height + T/B padding + T/B border + T/B margin
  • IE6 doesn't do this right

Document flow - block and inline elements

CSS properties for borders

h2 { border: 5px solid red; }

• thickness (specified in px, pt, em, or thin, medium, thick)
• style (none, hidden, dotted, dashed, double, groove, inset, outset, ridge, solid)
• color (specified as seen previously for text and background colors)

More border properties

Border example 2

h2 {
	border-left: thick dotted #CC0088;
	border-bottom-color: rgb(0, 128, 128);
	border-bottom-style: double;
}

• each side's border properties can be set individually
• if you omit some properties, they receive default values (e.g. border-bottom-width above)

Rounded corners with border-radius

p {
	border: 3px solid blue;
	border-radius: 12px;
	padding: 0.5em;
}

• each side's border radius can be set individually, separated by spaces

CSS properties for padding

Padding example 1

p { padding: 20px; border: 3px solid black; }
h2 { padding: 0px; background-color: yellow; }

Padding example 2

p {
	padding-left: 200px; padding-top: 30px;
	background-color: fuchsia;
}

• each side's padding can be set individually
• notice that padding shares the background color of the element

CSS properties for margins

Margin example 1

p {
	margin: 50px;
	background-color: fuchsia;
}

• notice that margins are always transparent
  (they don't contain the element's background color, etc.)

Margin example 2

p {
	margin-left: 8em;
	background-color: fuchsia;
}

• each side's margin can be set individually

CSS properties for dimensions

p { width: 350px; background-color: yellow; }
h2 { width: 50%; background-color: aqua; }

Notice what happens if we make the browser window wider or narrower

Centering a block element: auto margins

p {
	margin-left: auto;
	margin-right: auto;
	width: 550px;
}

• works best if width is set (otherwise, may occupy entire width of page)
• to center inline elements within a block element, use text-align: center;

Exercises

• Do Exercises Part 2 from the folder you checked out earlier