Related
I have a case where I must write inline CSS code, and I want to apply a hover style on an anchor.
How can I use a:hover in inline CSS inside the HTML style attribute?
E.g., you can't reliably use CSS classes in HTML emails.
Short answer: you can't.
Long answer: you shouldn't.
Give it a class name or an id and use stylesheets to apply the style.
:hover is a pseudo-selector and, for CSS, only has meaning within the style sheet. There isn't any inline-style equivalent (as it isn't defining the selection criteria).
Response to the OP's comments:
See Totally Pwn CSS with Javascript for a good script on adding CSS rules dynamically. Also see Change style sheet for some of the theory on the subject.
Also, don't forget, you can add links to external stylesheets if that's an option. For example,
<script type="text/javascript">
var link = document.createElement("link");
link.setAttribute("rel","stylesheet");
link.setAttribute("href","http://wherever.com/yourstylesheet.css");
var head = document.getElementsByTagName("head")[0];
head.appendChild(link);
</script>
Caution: the above assumes there is a head section.
You can get the same effect by changing your styles with JavaScript in the onMouseOver and onMouseOut parameters, although it's extremely inefficient if you need to change more than one element:
<a href="abc.html"
onMouseOver="this.style.color='#0F0'"
onMouseOut="this.style.color='#00F'" >Text</a>
Also, I can't remember for sure if this works in this context. You may have to switch it with document.getElementById('idForLink').
You could do it at some point in the past. But now (according to the latest revision of the same standard, which is Candidate Recommendation) you can't
.
You can't do exactly what you're describing, since a:hover is part of the selector, not the CSS rules. A stylesheet has two components:
selector {rules}
Inline styles only have rules; the selector is implicit to be the current element.
The selector is an expressive language that describes a set of criteria to match elements in an XML-like document.
However, you can get close, because a style set can technically go almost anywhere:
<html>
<style>
#uniqueid:hover {do:something;}
</style>
<a id="uniqueid">hello</a>
</html>
If you actually require inline code, this is possible to do. I needed it for some hover buttons, and the method is this:
.hover-item {
background-color: #FFF;
}
.hover-item:hover {
background-color: inherit;
}
<a style="background-color: red;">
<div class="hover-item">
Content
</div>
</a
In this case, the inline code: "background-color: red;" is the switch colour on hover. Use the colour you need and then this solution works. I realise this may not be the perfect solution in terms of compatibility, however this works if it is absolutely needed.
While it appears to be impossible to define a hover-rule inline, you can define the value of styles inline using a CSS variable:
:hover {
color: var(--hover-color);
}
<a style="--hover-color: green">
Library
</a>
Consider using an attribute or a class in addition to the selector (e.g., [hover-color]:hover) to allow coexistence with other low specificity hover color changing rules (from, e.g., a CSS reset or some elements using the default style).
Using JavaScript:
a) Adding inline style
document.head.insertAdjacentHTML('beforeend', '<style>#mydiv:hover{color:red;}</style>');
b) or a bit harder method - adding "mouseover"
document.getElementById("mydiv").onmouseover= function(e){this.className += ' my-special-class'; };
document.getElementById("mydiv").onmouseleave= function(e){this.className = this.className.replace('my-special-class',''); };
Note: multi-word styles (i.e.font-size) in JavaScript are written together:
element.style.fontSize="12px"
This is the best code example:
<a
style="color:blue;text-decoration: underline;background: white;"
href="http://aashwin.com/index.php/education/library/"
onmouseover="this.style.color='#0F0'"
onmouseout="this.style.color='#00F'">
Library
</a>
Moderator Suggestion: Keep your separation of concerns.
HTML
<a
style="color:blue;text-decoration: underline;background: white;"
href="http://aashwin.com/index.php/education/library/"
class="lib-link">
Library
</a>
JS
const libLink = document.getElementsByClassName("lib-link")[0];
// The array 0 assumes there is only one of these links,
// you would have to loop or use event delegation for multiples
// but we won't go into that here
libLink.onmouseover = function () {
this.style.color='#0F0'
}
libLink.onmouseout = function () {
this.style.color='#00F'
}
Inline pseudoclass declarations aren't supported in the current iteration of CSS (though, from what I understand, it may come in a future version).
For now, your best bet is probably to just define a style block directly above the link you want to style:
<style type="text/css">
.myLinkClass:hover {text-decoration:underline;}
</style>
Foo!
As pointed out, you cannot set arbitrary inline styles for hover, but you can change the style of the hover cursor in CSS using the following in the appropriate tag:
style="cursor: pointer;"
<style>a:hover { }</style>
Go Home
Hover is a pseudo class, and thus cannot be applied with a style attribute. It is part of the selector.
You can do this. But not in inline styles. You can use onmouseover and onmouseout events:
<div style="background: #333; padding: 10px; cursor: pointer"
onmouseover="this.style.backgroundColor='#555';" onmouseout="this.style.backgroundColor='#333';">
Hover on me!
</div>
According to your comments, you're sending a JavaScript file anyway. Do the rollover in JavaScript. jQuery's $.hover() method makes it easy, as does every other JavaScript wrapper. It's not too hard in straight JavaScript either.
There is no way to do this. Your options are to use a JavaScript or a CSS block.
Maybe there is some JavaScript library that will convert a proprietary style attribute to a style block. But then the code will not be standard-compliant.
You can write code in various type.
First I can write this
HTML
<a href="https://www.google.com/" onMouseOver="this.style.color='red'"
onMouseOut="this.style.color='blue'" class="one">Hello siraj</a>
CSS
.one {
text-decoration: none;
}
You can try another way:
HTML
Hello siraj
CSS
.one {
text-decoration: none;
}
.one:hover {
color: blue;
}
.one:active {
color: red;
}
You can also try hover in jQuery:
JavaScript
$(document).ready(function() {
$("p").hover(function() {
$(this).css("background-color", "yellow");
}, function() {
$(this).css("background-color", "pink");
});
});
HTML
<p>Hover the mouse pointer over this paragraph.</p>
In this code you have three functions in jQuery. First you ready a function which is the basic of a function of jQuery. Then secondly, you have a hover function in this function. When you hover a pointer to the text, the color will be changed and then next when you release the pointer to the text, it will be the different color, and this is the third function.
I just figured out a different solution.
My issue: I have an <a> tag around some slides/main content viewer as well as <a> tags in the footer. I want them to go to the same place in IE, so the whole paragraph would be underlined onHover, even though they're not links: the slide as a whole is a link. IE doesn't know the difference. I also have some actual links in my footer that do need the underline and color change onHover. I thought I would have to put styles inline with the footer tags to make the color change, but advice from above suggests that this is impossible.
Solution: I gave the footer links two different classes, and my problem was solved. I was able to have the onHover color change in one class, have the slides onHover have no color change/underline, and still able to have the external HREFS in the footer and the slides at the same time!
It's not exactly inline CSS, but it is inline.
<a href="abc.html" onMouseOver="this.style.color='#0F0'"
onMouseOut="this.style.color='#00F'">Text</a>
I agree with shadow. You could use the onmouseover and onmouseout event to change the CSS via JavaScript.
And don't say people need to have JavaScript activated. It's only a style issue, so it doesn't matter if there are some visitors without JavaScript ;)
Although most of Web 2.0 works with JavaScript. See Facebook for example (lots of JavaScript) or Myspace.
So this isn't quite what the user was looking for, but I found this question searching for an answer and came up with something sort of related. I had a bunch of repeating elements that needed a new color/hover for a tab within them. I use handlebars, which is key to my solution, but other templateing languages may also work.
I defined some colors and passed them into the handlebars template for each element. At the top of the template I defined a style tag, and put in my custom class and hover color.
<style type="text/css">
.{{chart.type}}-tab-hover:hover {
background-color: {{chart.chartPrimaryHighlight}} !important;
}
</style>
Then I used the style in the template:
<span class="financial-aid-details-header-text {{chart.type}}-tab-hover">
Payouts
</span>
You may not need the !important
While the "you shouldn't" context may apply there may be cases were you still want to achieve this. My use case was to dynamic set a hover color depending on some data value to achieve that with only CSS you can benefit from specificity.
Approach CSS only
CSS
/* Set your parent color for the inherit property */
.sidebar {
color: green;
}
/* Make sure your target element "inherit" parent color on :hover and default */
.list-item a {
color: inherit
}
.list-item a:hover {
color: inherit
}
/* Create a class to allows to get hover color from inline style */
.dynamic-hover-color:not(:hover) {
color: inherit !important;
}
Then your markup will be somewhat like:
Markup
<nav class="sidebar">
<ul>
<li class="list-item">
<a
href="/foo"
class="dynamic-hover-color"
style="color: #{{category.color}};"
>
Category
</a>
</li>
</ul>
</nav>
I'm doing this example using handlebars but the idea is that you take whatever is convenient for your use case to set the inline style (even if it is writing manually the color on hover you want)
You can just use an inline stylesheet statement like this:
<style>#T1:hover{color:red}</style><span id=T1>Your Text Here</span>
You can use the pseudo-class a:hover in external style sheets only. Therefore I recommend using an external style sheet. The code is:
a:hover {color:#FF00FF;} /* Mouse-over link */
You can do id by adding a class, but never inline.
<style>.hover_pointer{cursor:pointer;}</style>
<div class="hover_pointer" style="font:bold 12pt Verdana;">Hello World</div>
It is two lines, but you can reuse the class everywhere.
My problem was that I'm building a website which uses a lot of image-icons that have to be swapped by a different image on hover (e.g. blue-ish images turn red-ish on hover).
I produced the following solution for this:
.container div {
width: 100px;
height: 100px;
background-size: 100px 100px;
}
.container:hover .withoutHover {
display: none;
}
.container .withHover {
display: none;
}
.container:hover .withHover {
display: block;
}
<p>Hover the image to see it switch with the other. Note that I deliberately used inline CSS because I decided it was the easiest and clearest solution for my problem that uses more of these image pairs (with different URL's).
</p>
<div class=container>
<div class=withHover style="background-image: url('https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcQrqRsWFJ3492s0t0NmPEcpTQYTqNnH188R606cLOHm8H2pUGlH')"></div>
<div class=withoutHover style="background-image: url('http://i.telegraph.co.uk/multimedia/archive/03523/Cat-Photo-Bombs-fa_3523609b.jpg')"></div>
</div>
I introduced a container containing the pair of images. The first is visible and the other is hidden (display:none). When hovering the container, the first becomes hidden (display:none) and the second shows up again (display:block).
This question already has answers here:
Selecting and manipulating CSS pseudo-elements such as ::before and ::after using javascript (or jQuery)
(26 answers)
How to update placeholder color using Javascript?
(5 answers)
Closed 2 years ago.
Is it possible to change a CSS pseudo-element style via JavaScript?
For example, I want to dynamically set the color of the scrollbar like so:
document.querySelector("#editor::-webkit-scrollbar-thumb:vertical").style.background = localStorage.getItem("Color");
and I also want to be able to tell the scrollbar to hide like so:
document.querySelector("#editor::-webkit-scrollbar").style.visibility = "hidden";
Both of these scripts, however, return:
Uncaught TypeError: Cannot read property 'style' of null
Is there some other way of going about this?
Cross-browser interoperability is not important, I just need it to work in webkit browsers.
If you're comfortable with some graceful degradation in older browsers you can use CSS Vars. Definitely the easiest of the methods I've seen here and elsewhere.
So in your CSS you can write:
#editor {
--scrollbar-background: #ccc;
}
#editor::-webkit-scrollbar-thumb:vertical {
/* Fallback */
background-color: #ccc;
/* Dynamic value */
background-color: var(--scrollbar-background);
}
Then in your JS you can manipulate that value on the #editor element:
document.getElementById("#editor").style.setProperty('--scrollbar-background', localStorage.getItem("Color"));
Lots of other examples of manipulating CSS vars with JS here: https://eager.io/blog/communicating-between-javascript-and-css-with-css-variables/
To edit an existing one which you don't have a direct reference to requires iterating all style sheets on the page and then iterating all rules in each and then string matching the selector.
Here's a reference to a method I posted for adding new CSS for pseudo-elements, the easy version where you're setting from js
Javascript set CSS :after styles
var addRule = (function (style) {
var sheet = document.head.appendChild(style).sheet;
return function (selector, css) {
var propText = typeof css === "string" ? css : Object.keys(css).map(function (p) {
return p + ":" + (p === "content" ? "'" + css[p] + "'" : css[p]);
}).join(";");
sheet.insertRule(selector + "{" + propText + "}", sheet.cssRules.length);
};
})(document.createElement("style"));
addRule("p:before", {
display: "block",
width: "100px",
height: "100px",
background: "red",
"border-radius": "50%",
content: "''"
});
sheet.insertRule returns the index of the new rule which you can use to get a reference to it for it which can be used later to edit it.
EDIT: There is technically a way of directly changing CSS pseudo-element styles via JavaScript, as this answer describes, but the method provided here is preferable.
The closest to changing the style of a pseudo-element in JavaScript is adding and removing classes, then using the pseudo-element with those classes. An example to hide the scrollbar:
CSS
.hidden-scrollbar::-webkit-scrollbar {
visibility: hidden;
}
JavaScript
document.getElementById("editor").classList.add('hidden-scrollbar');
To later remove the same class, you could use:
document.getElementById("editor").classList.remove('hidden-scrollbar');
I changed the background of the ::selection pseudo-element by using CSS custom properties doing the following:
/*CSS Part*/
:root {
--selection-background: #000000;
}
#editor::selection {
background: var(--selection-background);
}
//JavaScript Part
document.documentElement.style.setProperty("--selection-background", "#A4CDFF");
You can't apply styles to psuedo-elements in JavaScript.
You can, however, append a <style> tag to the head of your document (or have a placeholding <style id='mystyles'> and change its content), which adjusts the styles. (This would work better than loading in another stylesheet, because embedded <style> tags have higher precedence than <link>'d ones, making sure you don't get cascading problems.
Alternatively, you could use different class names and have them defined with different psuedo-element styles in the original stylesheet.
I posted a question similar to, but not completely like, this question.
I found a way to retrieve and change styles for pseudo elements and asked what people thought of the method.
My question is at Retrieving or changing css rules for pseudo elements
Basically, you can get a style via a statement such as:
document.styleSheets[0].cssRules[0].style.backgroundColor
And change one with:
document.styleSheets[0].cssRules[0].style.backgroundColor = newColor;
You, of course, have to change the stylesheet and cssRules index. Read my question and the comments it drew.
I've found this works for pseudo elements as well as "regular" element/styles.
An old question, but one I came across when try to dynamically change the colour of the content of an element's :before selector.
The simplest solution I can think of is to use CSS variables, a solution not applicable when the question was asked:
"#editor::-webkit-scrollbar-thumb:vertical {
background: --editorScrollbarClr
}
Change the value in JavaScript:
document.body.style.setProperty(
'--editorScrollbarClr',
localStorage.getItem("Color")
);
The same can be done for other properties.
Looks like querySelector won't work with pseudo-classes/pseudo-elements, at least not those. The only thing I can think of is to dynamically add a stylesheet (or change an existing one) to do what you need.
Lots of good examples here:
How do I load css rules dynamically in Webkit (Safari/Chrome)?
This question already has answers here:
Selecting and manipulating CSS pseudo-elements such as ::before and ::after using javascript (or jQuery)
(26 answers)
How to update placeholder color using Javascript?
(5 answers)
Closed 2 years ago.
Is it possible to change a CSS pseudo-element style via JavaScript?
For example, I want to dynamically set the color of the scrollbar like so:
document.querySelector("#editor::-webkit-scrollbar-thumb:vertical").style.background = localStorage.getItem("Color");
and I also want to be able to tell the scrollbar to hide like so:
document.querySelector("#editor::-webkit-scrollbar").style.visibility = "hidden";
Both of these scripts, however, return:
Uncaught TypeError: Cannot read property 'style' of null
Is there some other way of going about this?
Cross-browser interoperability is not important, I just need it to work in webkit browsers.
If you're comfortable with some graceful degradation in older browsers you can use CSS Vars. Definitely the easiest of the methods I've seen here and elsewhere.
So in your CSS you can write:
#editor {
--scrollbar-background: #ccc;
}
#editor::-webkit-scrollbar-thumb:vertical {
/* Fallback */
background-color: #ccc;
/* Dynamic value */
background-color: var(--scrollbar-background);
}
Then in your JS you can manipulate that value on the #editor element:
document.getElementById("#editor").style.setProperty('--scrollbar-background', localStorage.getItem("Color"));
Lots of other examples of manipulating CSS vars with JS here: https://eager.io/blog/communicating-between-javascript-and-css-with-css-variables/
To edit an existing one which you don't have a direct reference to requires iterating all style sheets on the page and then iterating all rules in each and then string matching the selector.
Here's a reference to a method I posted for adding new CSS for pseudo-elements, the easy version where you're setting from js
Javascript set CSS :after styles
var addRule = (function (style) {
var sheet = document.head.appendChild(style).sheet;
return function (selector, css) {
var propText = typeof css === "string" ? css : Object.keys(css).map(function (p) {
return p + ":" + (p === "content" ? "'" + css[p] + "'" : css[p]);
}).join(";");
sheet.insertRule(selector + "{" + propText + "}", sheet.cssRules.length);
};
})(document.createElement("style"));
addRule("p:before", {
display: "block",
width: "100px",
height: "100px",
background: "red",
"border-radius": "50%",
content: "''"
});
sheet.insertRule returns the index of the new rule which you can use to get a reference to it for it which can be used later to edit it.
EDIT: There is technically a way of directly changing CSS pseudo-element styles via JavaScript, as this answer describes, but the method provided here is preferable.
The closest to changing the style of a pseudo-element in JavaScript is adding and removing classes, then using the pseudo-element with those classes. An example to hide the scrollbar:
CSS
.hidden-scrollbar::-webkit-scrollbar {
visibility: hidden;
}
JavaScript
document.getElementById("editor").classList.add('hidden-scrollbar');
To later remove the same class, you could use:
document.getElementById("editor").classList.remove('hidden-scrollbar');
I changed the background of the ::selection pseudo-element by using CSS custom properties doing the following:
/*CSS Part*/
:root {
--selection-background: #000000;
}
#editor::selection {
background: var(--selection-background);
}
//JavaScript Part
document.documentElement.style.setProperty("--selection-background", "#A4CDFF");
You can't apply styles to psuedo-elements in JavaScript.
You can, however, append a <style> tag to the head of your document (or have a placeholding <style id='mystyles'> and change its content), which adjusts the styles. (This would work better than loading in another stylesheet, because embedded <style> tags have higher precedence than <link>'d ones, making sure you don't get cascading problems.
Alternatively, you could use different class names and have them defined with different psuedo-element styles in the original stylesheet.
I posted a question similar to, but not completely like, this question.
I found a way to retrieve and change styles for pseudo elements and asked what people thought of the method.
My question is at Retrieving or changing css rules for pseudo elements
Basically, you can get a style via a statement such as:
document.styleSheets[0].cssRules[0].style.backgroundColor
And change one with:
document.styleSheets[0].cssRules[0].style.backgroundColor = newColor;
You, of course, have to change the stylesheet and cssRules index. Read my question and the comments it drew.
I've found this works for pseudo elements as well as "regular" element/styles.
An old question, but one I came across when try to dynamically change the colour of the content of an element's :before selector.
The simplest solution I can think of is to use CSS variables, a solution not applicable when the question was asked:
"#editor::-webkit-scrollbar-thumb:vertical {
background: --editorScrollbarClr
}
Change the value in JavaScript:
document.body.style.setProperty(
'--editorScrollbarClr',
localStorage.getItem("Color")
);
The same can be done for other properties.
Looks like querySelector won't work with pseudo-classes/pseudo-elements, at least not those. The only thing I can think of is to dynamically add a stylesheet (or change an existing one) to do what you need.
Lots of good examples here:
How do I load css rules dynamically in Webkit (Safari/Chrome)?
This question already has answers here:
How to reset/remove CSS styles for a specific element or selector only
(17 answers)
Closed last month.
I know this question was asked before, but before marking it as a duplicate, I want to tell you that my situation is a little different from what I found on the internet.
I'm building and embedded script that people can put it on their sites. This script creates a div with a certain width/height and some information in it.
My problem is that some websites declare styles for div that are inherited by my div as well.
for example:
div{
background-color:red;
}
so if I don't set any background color to my div, it will show red even if I don't want that.
The only solutions I come along is to overwrite as many css proprieties, this way my div will show exactly as I want.
The problem with this solution is that there are too many css proprieties to overwrite and I want my script to be as light as it can be.
So my question is if you know another solution to my problem.
It can be in css/javascript /jQuery.
Thanks
"Resetting" styles for a specific element isn't possible, you'll have to overwrite all styles you don't want/need. If you do this with CSS directly or using JQuery to apply the styles (depends on what's easier for you, but I wouldn't recommend using JavaScript/JQuery for this, as it's completely unnecessary).
If your div is some kind of "widget" that can be included into other sites, you could try to wrap it into an iframe. This will "reset" the styles, because its content is another document, but maybe this affects how your widget works (or maybe breaks it completely) so this might not be possible in your case.
Only set the relevant / important CSS properties.
Example (only change the attributes which may cause your div to look completely different):
background: #FFF;
border: none;
color: #000;
display: block;
font: initial;
height: auto;
letter-spacing: normal;
line-height: normal;
margin: 0;
padding: 0;
text-transform: none;
visibility: visible;
width: auto;
word-spacing: normal;
z-index: auto;
Choose a very specific selector, such as div#donttouchme, <div id="donttouchme"></div>. Additionally, you can add `!important before every semicolon in the declaration. Your customers are deliberately trying to mess up your lay-out when this option fails.
You could try overwriting the CSS and use auto
I don't think this will work with color specifically, but I ran into an issue where i had a parent property such as
.parent {
left: 0px;
}
and then I was able to just define my child with something like
.child {
left: auto;
}
and it effectively "reset" the property.
Technically what you are looking for is the unset value in combination with the shorthand property all:
The unset CSS keyword resets a property to its inherited value if it inherits from its parent, and to its initial value if not. In other words, it behaves like the inherit keyword in the first case, and like the initial keyword in the second case. It can be applied to any CSS property, including the CSS shorthand all.
.customClass {
/* specific attribute */
color: unset;
}
.otherClass{
/* unset all attributes */
all: unset;
/* then set own attributes */
color: red;
}
You can use the initial value as well, this will default to the initial browser value.
.otherClass{
/* unset all attributes */
all: initial;
/* then set own attributes */
color: red;
}
As an alternative:
If possible it is probably good practice to encapsulate the class or id in a kind of namespace:
.namespace .customClass{
color: red;
}
<div class="namespace">
<div class="customClass"></div>
</div>
because of the specificity of the selector this will only influence your own classes
It is easier to accomplish this in "preprocessor scripting languages" like SASS with nesting capabilities:
.namespace{
.customClass{
color: red
}
}
Try this: Create a plain div without any style or content outside of the red div. Now you can use a loop over all styles of the plain div and assign then to your inner div to reset all styles.
Of course this doesn't work if someone assigns styles to all divs (i.e. without using a class. CSS would be div { ... }).
The usual solution for problems like this is to give your div a distinct class. That way, web designers of the sites can adjust the styling of your div to fit into the rest of the design.
As long as they are attributes like classes and ids you can remove them by javascript/jQuery class modifiers.
document.getElementById("MyElement").className = "";
There is no way to remove specific tag CSS other than overriding them (or using another element).
you may use this below option.
<style>
div:not(.no_common_style){
background-color:red;
}
</style>
now , if their any place where you do not want to apply default style you can use 'no_common_style' class as class.
ex:
<div class="no_common_style">
It will not display in red
</div>
From what I understand you want to use a div that inherits from no class but yours. As mentioned in the previous reply you cannot completely reset a div inheritance. However, what worked for me with that issue was to use another element - one that is not frequent and certainly not used in the current html page. A good example, is to use instead of then customize it to look just like your ideal would.
area { background-color : red; }
One simple approach would be to use the !important modifier in css, but this can be overridden in the same way from users.
Maybe a solution can be achieved with jquery by traversing the entire DOM to find your (re)defined classes and removing / forcing css styles.
I have a CSS property (font) that I need to be able to change from Javascript (a pulldown). However, this font should only be used when printing (#media print).
So, the javascript can't just change the value of the font, because that will effect the screen view as well. Is there a way to change ONLY the print version of the font property?
Alternatively is there a way to have a CSS property be a reference to another property?
That way, in the print CSS, I could say font:printfont, and in the screen CSS font:12. And then change the value of printfont, and it would only change the font when printing.
thanks.
EDIT: The point is that I need to be able to change the font size that the document gets printed at from the pulldown, but I don't want to change the font size that the document gets displayed at.
That's an interesting dilemma you have going on there. Off the top of my head, the only thing I can think of is to add a new tag to the header where your font-size is declared with !important. For example, in your head tags:
<style type="text/css" media="print">
.printfont {
font-size: 16px !important;
}
</style>
This will ensure that the new font-size will take precedence.
The following is a very quick example of how you may accomplish this with javascript
<script type="text/javascript">
var inlineMediaStyle = null;
function changeMediaStyle ()
{
var head = document.getElementsByTagName('head')[0];
var newStyle = document.createElement('style');
newStyle.setAttribute('type', 'text/css');
newStyle.setAttribute('media', 'print');
newStyle.appendChild(document.createTextNode('.printFont { font-size: 16px !important;}'));
if (inlineMediaStyle != null)
{
head.replaceChild(newStyle, inlineMediaStyle)
}
else
{
head.appendChild(newStyle);
}
inlineMediaStyle = newStyle;
}
</script>
Just ensure that you have onchange="changeMediaStyle()" as an attribute on your dropdown. Also, as a disclaimer in my example, I am not accounting for things like memory leaks, so you will have to work out those kind of issues on your own.
As to your alternate question, as far as I am aware, there isn't any method for declaring/using what is essentially CSS variables. However, there is currently a recommendation out there for it: http://disruptive-innovations.com/zoo/cssvariables/
seems like what you want to do is myabe just change or add a class to the item with JS
<p class="inrto comicSans">this is the text to change</p>
#screen p.intro {font-family:verdana;}
#print p.comicSans {font-family:comic-sans;}
You could just use JavaScript to switch classes, and have the
#print {
.myPrintClass { font-family: serif; }
}
#screen {
.defaultClass { font-family: sans-serif; }
}
While the class-based solutions would totally work, you could also use Javascript to dynamically add a new <link> tag to the page. For instance, if you have:
stylesheet1.css:
#print * {font-family:verdana;}
stylesheet2.css:
#print * {font-family:comicSans;}
You could then use jQuery to do something like:
$(document.body).append("<link href='stylesheet2.css'/>");
(you could do it without jQuery too, but I forget that syntax and am too lazy to look it up ;-)).
However, if you're only changing small amounts, a single stylesheet + different classes is probably the better way to go; the new <link> tag solution is only worthwhile if you have a bunch of different style changes happening.