When you style the background of the body element, why does the styling affect the entire screen and not just the body element itself? Let's say I create the following rule:
body {
width: 700px;
height:200px;
border: 5px dotted red;
background-color: blue;
}
I find that the border shows up as 700px wide as I would expect, but the background color occupies the entire browser viewport. Why?
Quote from http://www.w3.org/TR/CSS21/colors.html
The background of the root element becomes the background of the canvas and covers the entire canvas, anchored (for 'background-position') at the same point as it would be if it was painted only for the root element itself. The root element does not paint this background again.
The body element is the root-element, and thus, as required by the CSS rules it loses its background style and the background style is applied to the containing canvas (the webpage area in the browser), therefor the entire screen is blue. The other properties stay with the element (e.g. the border).
From CSS: The Definitive Guide by Eric Meyer
In CSS values are never propagated
upward; that is, an element never
passes values up to its ancestors.
There is an exception to the upward
propagation rule in HTML: background
styles applied to the body element
can be passed to the html element,
which is the document's root element
and therefore defines its canvas.
So when you add the background-color: blue; declaration to the body element, this value is propagated to the html element (which is also the root element). Add this declartion to see it for yourself.
html {
background-color: grey;
}
When you set the background color of <body>, the browser interprets this as the background color for the entire window, even if you've forced the <body> to be smaller with CSS. Otherwise, what color would the outside of the <body> tag be?
This is why it's a good idea to use containers. Such as:
<body>
<div id="container">
</div>
</body>
Example here: http://jsfiddle.net/Shaz/2FqqV/
You cannot set a width on the <body> element itself, that's why the entire screen appears to be blue versus just a 700px area.
It must set the entire background, because you cannot define parts of the page that are "not" the body.
One of those mysteries of CSS, I guess.
A better idea is to place your content inside of a <div> element and style that instead of trying to style the whole <body> tag.
Related
$("#toggle").click(function(){
$("html").toggleClass("bg");
});
html.bg {
background: blue;
}
body {
background: yellow;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<!DOCTYPE html>
<html class="bg">
<head>
</head>
<body>
Test
<br>
<button id="toggle">Toggle HTML background</button>
</body>
</html>
I found that if you apply a CSS background to body, it takes up the whole page (no matter what the actual height or width of body is).
However, if you apply a CSS background to both html and body, the background for body does not take up the whole page.
Is this discrepancy expected behavior?
How would I go about superimposing two fullscreen backgrounds (say, a background color and a semi-transparent image?)
This is correct behavior.1 In standards mode, body, as well as html, doesn't immediately take up the entire height of the viewport, even though it appears so when you only apply a background to the latter. In fact, the html element will take on the background of body if you don't give it its own background, and html will pass this on to the canvas:
The background of the root element becomes the background of the canvas and its background painting area extends to cover the entire canvas, although any images are sized and positioned relative to the root element as if they were painted for that element alone. (In other words, the background positioning area is determined as for the root element.) If the root's ‘background-color’ value is ‘transparent’, the canvas's background color is UA dependent. The root element does not paint this background again, i.e., the used value of its background is transparent.
For documents whose root element is an HTML HTML element or an XHTML html element: if the computed value of ‘background-image’ on the root element is ‘none’ and its ‘background-color’ is ‘transparent’, user agents must instead propagate the computed values of the background properties from that element's first HTML BODY or XHTML body child element. The used values of that BODY element's background properties are their initial values, and the propagated values are treated as if they were specified on the root element. It is recommended that authors of HTML documents specify the canvas background for the BODY element rather than the HTML element.
That said, however, you can superimpose any background image over a background color on a single element (either html or body), without having to rely on two elements — simply use background-color and background-image or combine them in the background shorthand property:
body {
background: #ddd url(background.png) center top no-repeat;
}
If you wish to combine two background images, you need to rely on multiple backgrounds. There are chiefly two days to do this:
In CSS2, this is where styling both elements comes in handy: simply set a background image to html and another image to body which you wish to superimpose over the first. To ensure the background image on body displays at full viewport height, you need to apply height and min-height respectively as well:
html {
height: 100%;
background: #ddd url(background1.png) repeat;
}
body {
min-height: 100%;
background: transparent url(background2.png) center top no-repeat;
}
Incidentally, the reason why you have to specify height and min-height to html and body respectively is because neither element has any intrinsic height. Both are height: auto by default. It is the viewport that has 100% height, so height: 100% is taken from the viewport, then applied to body as a minimum to allow for scrolling of content.
In CSS3, the syntax has been extended so you can declare multiple background values in a single property, eliminating the need to apply backgrounds to multiple elements (or adjust height/min-height):
body {
background: url(background2.png) center top no-repeat,
#ddd url(background1.png) repeat;
}
The only caveat is that in a single multi-layered background, only the bottommost layer may have a background color. You can see in this example that the transparent value is missing from the upper layer.
And don't worry — the behavior specified above with propagating background values works exactly the same even if you use multi-layered backgrounds.
If you need to support older browsers, though, you'll need to go with the CSS2 method, which is supported all the way back to IE7.
My comments under this other answer explain, with an accompanying fiddle, how body is actually offset from html by default margins even though it looks like it's being padded out instead, again owing to this seemingly strange phenomenon.
1 This may have its roots in setting the HTML background and bgcolor attributes of body causing the background attribute to apply to the entire viewport. More on that here.
Suggest reading this:
https://css-tricks.com/just-one-of-those-weird-things-about-css-background-on-body/
Essentially, in the absence of a background on the html element, the body background will cover the page. If there is a background on the html element, the body background behaves just like any other element.
I have been investigating the way in which the html root element and the body child element
interact in an HTML document. The following excerpt in the CSS 2.1 specification states
that in the box model margins are transparent, which we all know.
http://www.w3.org/TR/CSS21/box.html#mpb-examples
The margins of the LI boxes are transparent — margins are always
transparent — so the background color (yellow) of the UL padding and
content areas shines through them.
However, what has made me curious is, if margins are transparent, then if I give
the root element, namely the html element, a margin, this margin should show through
the default browser user agent canvas color. However, this is not the case as shown by
the snippet below. The margin of the top-level html element seems to make use of the
same color as the one specified in its background property. Here is the code:
<!doctype html>
<html style="margin: 40px; border: 1px solid black; background: green;">
<head>
<meta charset="utf-8">
<title>Test</title>
<style type="text/css">
* { margin: 0; border: 0; padding: 0; }
</style>
</head>
<body style="margin: 40px; width: 400px; height: 300px; background: pink;">
</body>
</html>
Here we can see the green margin pertaining to the html root element, containing the
black border pertaining to the html root element, containing the green margin pertaining
to the body element, containing the pink content pertaining to the body element.
Is this behavior specified anywhere in the CSS 2.1 specification?
If so, then where? I can't seem to find it anywhere.
Thanks.
EDIT:
As BoltClock pointed out below, this behavior is mentioned in section 14.2 of the CSS 2.1
specification (and is carried on to the CSS3 spec's Background and Borders module). That
is, unlike for other CSS elements, the background of the html element also covers the
margins area.
However, as BoltClock also pointed out below, that section also specifies that it is
considered more appropriate to set the background color on the body element rather
than on the html element. Here is the relevant excerpt from the CSS 2.1 spec:
For HTML documents, however, we recommend that authors specify the
background for the BODY element rather than the HTML element. For
documents whose root element is an HTML "HTML" element or an XHTML
"html" element that has computed values of 'transparent' for
'background-color' and 'none' for 'background-image', user agents must
instead use the computed value of the background properties from that
element's first HTML "BODY" element or XHTML "body" element child when
painting backgrounds for the canvas, and must not paint a background
for that child element. Such backgrounds must also be anchored at the
same point as they would be if they were painted only for the root
element.
So let us try and see what happens if in our original HTML we comment
out the background CSS property from the html element's style attribute
as follows:
<!doctype html>
<html style="margin: 40px; border: 1px solid black; /* background: green; */">
<head>
<meta charset="utf-8">
<title>Test</title>
<style type="text/css">
* { margin: 0; border: 0; padding: 0; }
</style>
</head>
<body style="margin: 40px; width: 400px; height: 300px; background: pink;">
</body>
</html>
Here is the result:
As we can see, the pink background from the body element is propagated to the
entire html element's box, thus covering the html element's margin, the html
element's border (which is not pink but black because for the html element
the border we specified is solid and black), and the body's margin element
and the body's content area which appear as a single pink area (although
we could assign a background to the body element and it would cover the
content area of course).
In any case, this investigation has been carried out because of pure interest.
For all practical purposes you normally wouldn't set anything for the html
element and would just allow the rule "* { margin: 0; border: 0; padding: 0; }"
to be fall through to the html and body elements and apply a background on the
body element or within a wrapper div contained within the body element.
Regards.
Yes, it's in section 14.2:
The background of the root element becomes the background of the canvas and covers the entire canvas, anchored (for 'background-position') at the same point as it would be if it was painted only for the root element itself. The root element does not paint this background again.
It's mentioned again in section 3.11 of the Backgrounds and Borders module, which supercedes this section of CSS2.1, so this specific behavior remains unchanged.
Since you mention interactions between the html and body elements, note that both links also contain details on how the body background should be propagated to the root element in certain circumstances when rendering an HTML document. And for those curious, all browsers follow this to the letter; it's based on the traditional behavior of painting the entire canvas with the background when you set the background and bgcolor attributes on the body element, so it's basically traditional HTML behavior specified in terms of CSS (to maintain backward compatibility with legacy sites if nothing else).
I'm writing a very simple css code which is listed below:
body {
background-color:#616161;
margin-left: 20%;
}
Even though I've specified a 20% margin on the left side, the background color affects the margin area of the body tag as well. How do I ensure that the background color remains within the border?
Use a div to put the background color in
<html>
<body>
<div class="background">
<p>This is some text</p>
</div>
</body>
</html>
Then use this CSS to assign the color and the margin, you have to tweak the code to get the width and height where you want it
html{
height:100%;
}
body{
height:100%;
margin-top:0px;
margin-left: 20%;
}
.background{
min-height:100%;
height:auto;
background-color:#616161;
width:100%;
}
Or as miro pointed out:
html { background-color:#fff; }
body {
background-color:#616161;
margin:0% 0% 0% 20%;
}
Found nice description for this browser behaviour: "Background properties on the body element will propagate to the html element (the viewport), but only if the latter’s computed value for the background property is transparent." (link) + (testing fiddle).
The best solution here is to use the additional div just like user2067005 has suggested above.
W3C recommends:
For HTML documents, however, we recommend that authors specify the background for the BODY element rather than the HTML element. For documents whose root element is an HTML "HTML" element or an XHTML "html" element that has computed values of 'transparent' for 'background-color' and 'none' for 'background-image', user agents must instead use the computed value of the background properties from that element's first HTML "BODY" element or XHTML "body" element child when painting backgrounds for the canvas, and must not paint a background for that child element. Such backgrounds must also be anchored at the same point as they would be if they were painted only for the root element. (link)
Relevant JS Fiddle http://jsfiddle.net/arosen/FMQtR/
Problem
My HTML looks something like this:
<div id='parent'>
<div id='one'>
A variable amount of text here.
</div>
<div id='two'>
A less important variable amount of text here.
</div>
</div>
The #parent div is a fixed height and cannot change. Within it, I have at least two child divs. The first one (or many) will have an unknown amount of text in it determining its height. Based on the content of the first one, I want the last one to take up as much height is left in the parent but not overflow.
My current example CSS is:
#parent {
border: 1px solid #000;
height: 150px;
width: 150px;
}
#one, #two {
border: 1px dashed #333;
height: auto;
margin: 5px;
padding: 5px;
overflow: hidden;
}
My current JS solution
function() {
var $two = $('#two');
var $parent = $('#two').parent()
$parent.css('overflow', 'hidden');
var heightDifference = $parent[0].scrollHeight - $parent.height();
$two.css('height', $two.height() - heightDifference);
}
I'm wondering if there is a CSS layout or HTML solution to this problem or if I must use the JS solution I have in the fiddle that is run on the push of the last button.
EDIT Updated my JS fiddle as the text will not change once on the page but depending on information loaded from the server, will not know how much text it will have until the page is rendered.
EDIT 2 Only modern (and IE 9) browsers need to be supported.
EDIT 3 The final div must have a height as it is used by other jQuery plugins.
No. You can't. CSS isn't a programming language. Instead every selector{ property:value; } tuple defines a rule for a specific set of elements. The actual style such as current height, current width or other properties cannot be accessed in CSS.
Someone might think "what about percentage values"? Well, those are based on the containing block, which is often the parent element (in this case #parent).
So you either have to specify a fixed height for all div (which isn't possible according to the information you gave us), or use a JavaScript based solution.
You could accomplish this if you're not too set on borders/margin/padding/line-height. Just make sure that (parent div - (all margins/padding)) is wholly divisible by your line-height, you'd never see partial lines or overflow. However, with your border styles you can't achieve this through CSS alone.
You could still hack it by adding another element to the parent div, say a paragraph tag with the dashed border-top, and a thick white bottom border, positioned to hide the overflowing border with the above solution... but that's hacky, which I'm not a fan of, and has a potential to break easily across browsers.
TL;DR - Just use your JS.
I need to place an icon of 48x48 as background. I have this icon in my image sprite where of course there are many other images.
Is there a way to show as background only a porition of the image?
thanks
EDIT: Is there a way to do this without setting width-height of the backgrounded element? (I am not sure if acutally i can set a width-height)
Edit2: this is what i need: http://jsfiddle.net/pdxnj/
Thanks
Set the width and height of the element to 48px.
.element{
width: 48px;
height: 48px;
}
Set the background of the element to your image
.element{
background-image: url('image.png');
}
Move the background so that the top left corner of the icon is positioned correctly.
.element{
background-position: 20px 94px;
}
The two numbers in background-position are the X and Y coordinates (respectively) where the top left corner of your 48px by 48px is in your sprite image. So maybe it's actually 96px 0px or something.
EDIT
If you can't control the width and height of the element you are trying to put the background in, but you can add new DOM elements, you can try adding a span inside the element you really want to put the image as a background for.
It would look something like:
<div id="noControl">
<span id="justCreated">
</span>
</div>
and the CSS would look exactly the same as above, except you would need to treat the inline span as a block element:
#justCreated{
display: inline-block;
}
EDIT 2
If you have control over new DOM elements, and want to make your sprite the background without messing with a span, just add another div inside your original one.
Would wind up looking like:
<div id="noControl">
<div id="justCreated">
ALL of the content that used to be inside #noControl
</div>
</div>
and the CSS for it would be
#justCreated{
width: 48px;
height: 48px;
background-image: url('image.png');
background-position: 96px 0px;
z-index: -200;
/* z-index of all the contents needs to be not set, or set to larger than -200 */
}
This is all theoretical, but it SHOULD work.
This way, you can apply the sprite sizing to a block element without messing with the inline stuff. This may affect CSS if it addresses elements by child status (like #noControl > a), because you are inserting a div between the parent and the child.
I am still researching whether you can do this at all if you have no control over the DOM at all.
simple answer no, but by using html elements you can. Html element hight and width should match the background portion of image.
You can if you're not going to be setting a repeating background. Otherwise no.
To do this, you need to play around with the background offset, and width/height of the actual element that you're setting the background on.
it will depend on how much whitespace is around it in the sprite whether it will fit where you need it to without showing parts of other images.. however you could e.g. put a span where you want the image and crop the span to 48x48 so that it only shows the icon itself. it kind of depends what you want to use it for and how the sprite is built
It's better using ::before or ::after so you can easily define your image size without having overflow problems!
This is possible. You need to display that in a 48x48 div then set position: absolute style for the div and define left and top too for it. Also set z-index: 0 for the div so that it appears under everything.