This chapter is from the book
This chapter is from the book
This chapter is from the book
Defining Styles Based on Context
Contextual styles allow you to specify how a particular element should appear based on its parents and siblings. For example, you may want an emphasis tag to appear one way when it’s in the main header of the page and differently when it appears in the sub-header. You may want still another appearance in a paragraph of text. These combinatory selectors (Table 4.1) are among the most used and useful in CSS.
Table 4.1. Combinatory Selectors
|
Format |
Selector Name |
Elements Are Styled If... |
|
|
|
|
|
|
a b c |
Descendent |
c descendent of b descendent of a |
|
|
|
|
|
|
a * b |
Universal |
b within a regardless of b’s parents |
|
|
|
|
|
|
a > b |
Direct child |
b direct child of a |
|
|
|
|
|
|
a + b |
Adjacent sibling |
sibling b immediately after a |
|
|
|
|
|
|
a ~ b |
General sibling |
sibling b anywhere after a |
|
|
|
|
|
Styling descendents
You can style individual descendent elements depending on their parent selector or selectors in a space-separated list. The last selector will receive the style if and only if it is the descendent of the preceding selectors 
.
)
When you want to indicate that the exact selector does not matter at any given level, you can use the universal selector (*) described in Chapter 3 
.
)
The general syntax for the descendent selector using the universal selector.
To style descendent elements
- Set up a list of descendent selectors. Type the HTML selector of the parent tag, followed by a space, and then the final child or another parent (Code 4.1).
article.chaptertext p strong em {...}You can type as many HTML selectors as you want for as many parents as the nested tag will have, but the last selector in the list is the one that receives all the styles in the rule.
- Styles will be used only if the pattern is matched.
<article class="chaptertext"><p><strong><em>...</em></strong></p></article>
The style will be applied if and only if the final selector occurs as a descendent nested within the previous selectors. So, in this example, the emphasis tag (em) is styled only if it is in a paragraph (strong) that is within a paragraph tag (p), that is in an article tag using the class chaptertext (article.chaptertext).
The emphasis tag would not be styled by the code in Step 1 in the following case, because it is not in a strong tag:
<article class="chaptertext"><p><em>...</em></p></article>
And emphasis will not be styled by the code in Step 1 in the following case because the article tag does not have the chaptertext class:
<article><p><strong><em>...</em></strong></p></article>
It is important to note, though, that although the selectors do not style the emphasis tag in these last two cases, it does not mean that styles from other declarations will not do so.
Code 4.1. The style is set for the emphasis tag if its parents are the h1 tag and the article tag using the copy class 
.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Alice’s Adventures in Wonderland</title>
<style type="text/css" media="all">
article.chaptertext p strong em {
color: red;
font-weight: normal;
font-size: 2em;
font-style: normal; }
</style>
</head>
<body>
<article class="chaptertext">
<p><strong>Alice was beginning to get <em>very tired</em> of sitting by her sister on the bank,
→ </strong> and of having nothing to do: <strong>once or twice</strong> she had peeped into the
→ book her sister was reading, but it <em>had no pictures or conversations in it</em>, <q>and
→ <em>what</em> is the use of a book,</q> <strong>thought Alice</strong>, <q>without pictures or
→ conversations?</q></p>
</article>
</body>
</html>
)
The results of Code 4.1. The only text that meets the selective criteria is in red, which is only the emphasis tag in the h1, in this example.
To style descendents universally
- Set up a list of descendent selectors including a universal selector. Type the HTML selector of the parent tag, followed by a space, and then an asterisk (*) or other selectors (Code 4.2).
article.chaptertext p * em {...} - Styles will be used only if the pattern is matched. Generally, the universal selector is used at the end of a list of selectors so that the style is applied explicitly to all of a parent’s direct descendents (children). However, the styles will not be directly applied to those children’s descendents.
In this example, the style is applied to the emphasis tag inside any parent tag (such as strong) in a paragraph, such as:
<article class="chaptertext"><p><strong><em>...</em></strong></p></article>
Or:
<article class="chaptertext"><p><q><em>...</em></q></p></article>
However, an emphasis tag that is not in another tag in the paragraph will not be styled.
<article class="chaptertext"><p><em>...</em></p></article>
Code 4.2. The style is set for the emphasis tag with any parent that’s in an article tag using the copy class 
.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Alice’s Adventures in Wonderland</title>
<style type="text/css" media="all">
article.chaptertext p * em {
border: 1px double red;
font-size: 2em;
font-weight: normal; }
</style>
</head>
<body>
<article class="chaptertext">
<p><strong>Alice was beginning to get <em>very tired</em> of sitting by her sister on the bank,
→ </strong> and of having nothing to do: <strong>once or twice</strong> she had peeped into the
→ book her sister was reading, but it <em>had no pictures or conversations in it</em>, <q>and
→ <em>what</em> is the use of a book,</q> <strong>thought Alice</strong>, <q>without pictures or
→ conversations?</q></p>
</article>
</body>
</html>
)
The results of Code 4.2. The text in red matches the selective criteria with the universal selector. In this case, all emphasis tags match.
Styling only the children
If you want to style only a parent’s child elements (not a grandchild descendent), you must specify the parent selector and child selector, separated by a right angle bracket (>) 
.
)
To define child selectors
- Set up a list of direct child selectors. Type the selector for the parent element (HTML, class, or ID), followed by a right angle bracket (>) and the child selector (HTML, class, or ID).
article.chaptertext > p > em {...}You can repeat this as many times as you want with the final selector being the target to which you apply the styles (Code 4.3). You can have one space between the selector and the greater-than sign or no spaces.
- Styles are used only if the pattern is matched.
<article class="chaptertext"><p><em>...</em></p></article>
The styles from Step 1 are applied if and only if the final selector is an immediate child element nested in the preceding element. Placing the tag within any other HTML tags will disrupt the pattern. In this example, the emphasis tag (em) is styled only if it is in a paragraph (p) within an article (article).
However, any emphasis tag that is in another tag will not be styled:
<article class="chaptertext"><p><q><em>...</em></q><p></article>
Code 4.3. The style is applied to the emphasis tag only if it is a child of a paragraph that is in turn the child of an article tag using the copy class 
.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Alice’s Adventures in Wonderland</title>
<style type="text/css" media="all">
article.chaptertext > p > em {
color: silver;
background: red;
font-size: 2em;
font-weight: normal; }
</style>
</head>
<body>
<article class="chaptertext">
<p><strong>Alice was beginning to get <em>very tired</em> of sitting by her sister on the bank,
→ </strong> and of having nothing to do: <strong>once or twice</strong> she had peeped into the
→ book her sister was reading, but it <em>had no pictures or conversations in it</em>, <q>and
→ <em>what</em> is the use of a book,</q> <strong>thought Alice</strong>, <q>without pictures or
→ conversations?</q></p>
</article>
</body>
</html>
)
The results of Code 4.3. The text in red matches the direct child criteria. In this case the emphasis tags match within the paragraphs but not within the headers.
Styling siblings
Siblings are elements that have the same parent. You can style a sibling that is immediately adjacent to another 
or occurs anywhere after that sibling 
.
)
)
To define adjacent sibling selectors
- Set up a list of adjacent sibling selectors. Type the selector for the first element (HTML, class, or ID), a plus sign (+), and then the selector (HTML, class, or ID) for the adjacent element to which you want the style applied (Code 4.4).
strong + em {...} - Styles will be used only if the pattern is matched.
<strong>...</strong>...<em>...</em>
The styles will be applied to any sibling that occurs immediately after the preceding selector with no other selectors in the way. Placing any element between them (even a break tag) will disrupt the pattern. The following pattern will not work:
<strong>...</strong>...<q>...</q>...<em>...</em>
Code 4.4. The style is applied to the emphasis tag only if it is in a paragraph that is immediately after another paragraph 
.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Alice’s Adventures in Wonderland</title>
<style type="text/css" media="all">
strong + em {
color: red;
background: silver;
font-size: 2em; }
</style>
</head>
<body>
<article class="chaptertext">
<p><strong>Alice was beginning to get <em>very tired</em> of sitting by her sister on the bank,
→ </strong> and of having nothing to do: <strong>once or twice</strong> she had peeped into the
→ book her sister was reading, but it <em>had no pictures or conversations in it</em>, <q>and
→ <em>what</em> is the use of a book,</q> <strong>thought Alice</strong>, <q>without pictures or
→ conversations?</q></p>
</article>
</body>
</html>
)
The results of Code 4.4. The text in red matches the adjacent sibling criteria—the emphasis tags within the second and third paragraphs in this case—but does not match the fourth paragraph because a block quote is in the way.
To define general sibling selectors
- Set up a list of general sibling selectors. Type the selector for the first sibling element (HTML, class, or ID), a tilde sign (~), and then another selector (HTML, class, or ID) (Code 4.5).
strong ~ em {...}You can repeat this as many times as necessary, but the last selector in the list is the one you are targeting to be styled.
- Styles are used only if the pattern is matched.
<strong>...</strong>...<em>...</em>...<q>...</q>...<em>...</em>
The styles are applied to any siblings that occur after the first sibling selector, not just the first one. Unlike the adjacent sibling, this is true even when other types of tags are located in between. In the case above, this includes both the second and third strong tags
Table 4.2. Universal Selector Examples
|
Format |
Elements Are Styled If... |
|
a * b |
b within a regardless of b’s parents |
|
a > * > b |
b is the direct child of any element that is the direct child of a |
|
a + * + b |
sibling b immediately after any element that is immediately after a |
|
*:hover |
mouse pointer over any element |
|
*:disabled |
any element that is disabled |
|
*:first-child |
first child of any element |
|
*:lang() |
any element using specified language code |
|
*:not(s) |
any element that is not the using indicated selectors |
|
*::first-letter |
any element’s first letter |
Code 4.5. The style is applied to the emphasis tag if it is in a paragraph with any preceding sibling that is a paragraph 
.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Alice’s Adventures in Wonderland</title>
<style type="text/css" media="all">
strong ~ em {
color: red;
background: gray;
font-size: 2em; }
</style>
</head>
<body>
<article class="chaptertext">
<p><strong>Alice was beginning to get <em>very tired</em> of sitting by her sister on the bank,
→ </strong> and of having nothing to do: <strong>once or twice</strong> she had peeped into the
→ book her sister was reading, but it <em>had no pictures or conversations in it</em>, <q>and
→ <em>what</em> is the use of a book,</q> <strong>thought Alice</strong>, <q>without pictures or
→ conversations?</q></p>
</article>
</body>
</html>
)
The results of Code 4.5. The text in red matches the general sibling criteria—in this case the emphasis tags within the second, third, and fourth paragraphs.