Regarding float, MDN says:
The element is removed from the normal flow of the page, though still remaining a part of the flow (in contrast to absolute positioning).
But it does not expand on that at all.
So I did a simple experiment. It seems when the floated element has an inline sibling, it is still part of the normal flow, allowing text and inline elements to wrap around it. But for block siblings, the floated element collapsed to have a zero height.
This behavior is further confirmed in the spec. For content (inline elements I guess?) -
The most interesting characteristic of a float (or "floated" or "floating" box) is that content may flow along its side (or be prohibited from doing so by the 'clear' property). Content flows down the right side of a left-floated box and down the left side of a right-floated box.
And for block boxes -
Since a float is not in the flow, non-positioned block boxes created before and after the float box flow vertically as if the float did not exist.
This does not feel intuitive nor consistent. Why was this design choice?
Related
Let's say that I want to make a <p> element that has a fixed height and a width that only grows if the height is not sufficient to display all of the text. By default, <p> is a block level element. This means it has a greedy width and lazy height. I want the opposite, lazy dynamic width and fixed/greedy height. An inline-block element tries to display the text in one line if possible, which is not something I want. I want a pure CSS solution just because. Is it possible?
This is not possible.
9.4.2 Inline formatting contexts
In an inline formatting context, boxes are laid out horizontally
[...]. The rectangular area that contains the boxes that form a line
is called a line box.
The width of a line box is determined by a containing block and the
presence of floats. [...]
In general, the left edge of a line box touches the left edge of its
containing block and the right edge touches the right edge of its
containing block. However, floating boxes may come between the
containing block edge and the line box edge. Thus, although line boxes
in the same inline formatting context generally have the same width
(that of the containing block), they may vary in width if available
horizontal space is reduced due to floats. [...]
Line boxes are created as needed to hold inline-level content within
an inline formatting context. [...]
Therefore, the width of the line boxes will only be affected by the width of the containing block and the presence of floats. And then, there will be as many line boxes as necessary.
I'm pretty CSS-savvy, but I'm seeing some odd float/clear behavior. I have it working, but I'm not entirely sure why and am looking for an explanation.
JSFiddle: http://jsfiddle.net/ismyrnow/JV5n6/
I have a 2 column layout - sidebar and content - where the sidebar is floated but the content is not; the content div has a left margin applied to it.
If I use clear:both on any elements in the content div, the element unexpectedly drops below the height of the sidebar div (unexpectedly because the floated sidebar isn't directly affecting the positioning of items inside the content area).
What is even more unexpected, is that when I add overflow:auto to the content div, the problem goes away. (I found the solution here)
Can someone explain:
Why clear:both would cause an element to clear a floated element that isn't directly affecting its position.
Why overflow:auto on the parent element fixes the issue.
Why clear:both would cause an element to clear a floated element that isn't directly affecting its position.
It may not be directly affecting its position, but it would still have affected it anyway, because in the absence of any clearance, floats aren't normally restricted in how they affect the rest of the normal flow layout even once they are taken out of it, not even by different parent elements such as your .b content element with the left margin in this case. The only real restriction is that floating elements may only affect elements that come after them in document tree order, i.e. elements that are following (not preceding) siblings, as well as their descendants.
The content that's just above the element within your content column isn't tall enough to push it beneath the floated element. If you remove that declaration, you would see that both .c elements become positioned next to their respective floats as well.
When you add clear, what happens is that it forces the clearing element to be positioned beneath the float regardless of where it ends up horizontally.
Why overflow:auto on the parent element fixes the issue.
This is because any block boxes with overflow other than visible generate block formatting contexts. A property of a block formatting context is that floating boxes outside it can never interact with any boxes inside it, and vice versa.
Once you cause the content element to establish its own block formatting context, your floating element is no longer able to affect any elements inside the content element (see the section on the float property), and the clearing element inside it is no longer able to clear any floats that are outside the content element (see the clear property).
For clear:both
The clear CSS property specifies whether an element can be next to floating elements that precede it or must be moved down (cleared) below them.
The clear property applies to both floating and non-floating elements.
When applied to non-floating blocks, it moves the border edge of the element down until it is below the margin edge of all relevant floats. This movement (when it happens) causes margin collapsing not to occur.
When applied to floating elements, it moves the margin edge of the element below the margin edge of all relevant floats. This affects the position of later floats, since later floats cannot be positioned higher than earlier ones.
The floats that are relevant to be cleared are the earlier floats within the same block formatting context.
I hope this will clear your doubt.
This is the link from where i found the above info.....
https://developer.mozilla.org/en-US/docs/Web/CSS/clear
I'm following In Search of the Holy Grail, but am having trouble understanding what's actually going on in step 3.
To break the problem down, I disabled the margins/offsets of the "left" and "right" divs. This gives you the content at the top, and then the two other elements sitting side by side under it as I would expect [see P1].
I then gradually decreased the margin-left of the "left" div from 0px to -199px which again does what I expect [see P2].
But at -200px (the width of the left element itself), it shoots up to the top [see P3], with the left edge against the right edge of the content. I would have expected it to just keep going off the edge.
Why does it jump up? And if there's no conceptual explanation as to why, where does it describe that functionality in the spec?
Images:
P1
P2
P3
Remember that both #content and #left (as well as #right) are floated.
Due to the nature of floats, they (or their contents) may overlap. This is well described in this section of the spec, and is fairly easy to understand. If you apply negative margins to a floated element that's adjacent to another float, it will simply move to its left (similar to having a left relative offset), over its sibling.
In the section on the float property, you'll find a list of "the precise rules that govern the behavior of floats." Now, I'm not 100% familiar with the float model, but these points are what I believe to be relevant:
2. If the current box is left-floating, and there are any left-floating boxes generated by elements earlier in the source document, then for each such earlier box, either the left outer edge of the current box must be to the right of the right outer edge of the earlier box, or its top must be lower than the bottom of the earlier box. Analogous rules hold for right-floating boxes.1
7. A left-floating box that has another left-floating box to its left may not have its right outer edge to the right of its containing block's right edge. (Loosely: a left float may not stick out at the right edge, unless it is already as far to the left as possible.) An analogous rule holds for right-floating elements.
8. A floating box must be placed as high as possible.
9. A left-floating box must be put as far to the left as possible, a right-floating box as far to the right as possible. A higher position is preferred over one that is further to the left/right.
So my guess is: a margin of -200px, which is as you say the negative equivalent of the width of the #left element itself, causes it to float all the way up and to the right (rather than to the left) and to hug the edge of the #center element which itself is also floated. The right edge of both elements touch each other because of this full, equal negative margin. Consequently, as you continue to increase (or decrease?) the negative margin, you'll see that the #left element continues to move to its left.
Note that the padding applied to the #container element doesn't interact with the margins; even if you remove the padding on either side or both sides, the margins will interact in the same way.
1 Note also that there's a statement in the section on collapsing margins in the linked section of the spec, that describes the behavior of negative margins, but that is irrelevant as the margins we are concerned with here are horizontal and belong to floated elements, and so are never affected by collapsing.
you are using <h2> tag for left and right heading but in center you are using <h1> that's why you have this problem if you want to solve this problem do one thing 1 use all <h2> tag for heading and if you want to use then apply below class on
h1
{
margin-top:10px;
}
Which CSS rules explain the following sceanrio:
Assuming I have the following HTML CSS snippets
HTML:
<div id="main">
<div id="first">
first div float left
</div>
<div id="second">
second div does not have a float property set
and appears in a new line instead of next to
the first div
</div>
</div>
CSS:
#first
float: left
What I am wondering about is, why the second div floats next to the first div, only when its width is set. If I replace the second div with a paragraph, it also floats next the first div. So why does the second div only position next to the first one when its width is set or its own float property is set to float left?
By the way. I am not trying to achieve any sort of layout here. I am just trying to understand these particular behaviours of the div element and other block elements.
EDIT:
OK. First of all thanks for the answers. The problem I had was based on the fact that I did set the width of the first and the second div to the same value, so that the content of the second could not float around the first one. To sum things up, I guess it is important to know that elements with the float property set are taken put of the page flow and dont take up any space. Secondly one should remember only the content can flow around, not the actual div.
A <div> is a block level element which is 100% wide and has a line break before & after when it's within the normal content flow.
Technically, when you float a <div>, you're taking the element out of the normal flow so it no longer has a line-break before & after and also the other page content flows around it.
So why does the second div only position next to the first one when
its width is set or its own float property is set to float left?
Floated <div>'s will always appear side-by-side only if there's enough room to contain them side-by-side. Otherwise, the next floated <div> will wrap to a new line. This is because floated <div>'s are outside the content flow and defined to behave this way in the spec.
However, you've made some incorrect assumptions in your question about what happens when you set the width of the second (non-floated) <div>.
The second <div>, itself, is always underneath (meaning behind) the floated <div>. Whereas, the "content" of the second <div> always flows around the floated <div>. (see three examples below)
So whether or not you set the width of the second div, its content will still flow around the left floated div as you can see illustrated here in three examples. (For illustration purposes, the first <div> is red with 50% opacity and the second is blue with a thick green border.)
Fiddle with second div wider than first
Fiddle with no set width (100%) on second div
Fiddle with second div narrower than first
As you can see from all three examples above, despite the existence of the floated first <div>...
the second <div> always starts on the left edge of the screen despite the width of the second <div>.
the second <div> always starts on the top edge of the screen because there's no other page flow content above the second <div>.
the actual content of the second <div> flows around (to the right of) the floated first <div> only where there is enough room inside its container to allow it to flow around the floated <div>. Otherwise, it appears as if it's starting a new line where really only its content is continuing to flow around the bottom of the floated <div>.
W3C Spec: 9 Visual formatting model, 9.5 Floats
A float is a box that is shifted to the left or right on the current
line. The most interesting characteristic of a float (or "floated" or
"floating" box) is that content may flow along its side (or be
prohibited from doing so by the 'clear' property). Content flows down
the right side of a left-floated box and down the left side of a
right-floated box. The following is an introduction to float
positioning and content flow; the exact rules governing float behavior
are given in the description of the 'float' property.
A floated box is shifted to the left or right until its outer edge
touches the containing block edge or the outer edge of another float.
If there is a line box, the outer top of the floated box is aligned
with the top of the current line box.
If there is not enough horizontal room for the float, it is shifted
downward until either it fits or there are no more floats present.
Since a float is not in the flow, non-positioned block boxes created
before and after the float box flow vertically as if the float did not
exist. However, the current and subsequent line boxes created next to
the float are shortened as necessary to make room for the margin box
of the float.
And here are a whole bunch of examples...
W3C Spec: 9 Visual formatting model, 9.8 Comparison of normal flow, floats, and absolute positioning
What makes you believe the div's are floated next to each other? In reality they are not. It's only that their content shows up next to each other but that's not because DIV #second is to the left of the floated DIV. It doesn't matter if you set the width or not.
What in fact is happening is that the floated DIV #first is floated to the left. Because it's floated, it's taken out of the normal flow. This means that DIV #second is actually on the same place as where DIV #first is appearing. The content of DIV #second though is inline content and inline content always flows around floated elements. Even floated elements that are outside of the container. So DIV #second is underneath DIV #first but the content of DIV #second is floating around DIV #first.
To illustrate that, I've create this CSS:
#first { float: left; background-color: rgba(255,0,0,0.3); }
#second { background-color: rgba(0,255,0,1); }
Play with the alpha value of the RGBA() value (i.e. the last parameter, it can range from 0 to 1) of the background-color of DIV #first and you will see that DIV #second is in fact below DIV #first all the time
Unless you clear your floats, the next block level element will float next to the last float by default.
I'm not sure what you're trying to achieve here, but if you want #first to float, and #second to NOT float, the rule you'd want to add to #first is : clear:both
But, that's pretty silly, you might as well just remove the float properties completely if you want to stack them.
Block elements take 100% of the width of their parent element, so even if your first div is floated, the second div will take the width of his parent, thus falling on a second line. This is why if you specify a smaller width, it stands next to the first floated div.
The reason why it also works if you float the two divs is that floated element behave a bit more like inline-block elements, wich means they will only take the space needed for the content inside of them.
Bottom line is, if you want these two divs to stand next to each other, you should probably just float the two of them.
I have the following CSS:
label{
float:left;
margin-left:24px;
}
button{
margin-left:24px;
}
for this HTML:
<label>
<input>
</label>
<button>
and I was hoping that the button was found at a distance of 24 pixels of the label, however this did not happen until I floated the button to the left too. What part of the CSS specification I can refer to understand why this happening?
(Please, sorry my English.)
Just read the W3C documentation for float:
Here are the precise rules that govern
the behavior of floats:
The left outer edge of a left-floating box may not be to the
left of the left edge of its
containing block. An analogous rule
holds for right-floating elements.
If the current box is left-floating, and there are any
left-floating boxes generated by
elements earlier in the source
document, then for each such earlier
box, either the left outer edge of the
current box must be to the right of
the right outer edge of the earlier
box, or its top must be lower than the
bottom of the earlier box. Analogous
rules hold for right-floating boxes.
The right outer edge of a left-floating box may not be to the
right of the left outer edge of any
right-floating box that is next to it.
Analogous rules hold for
right-floating elements.
A floating box's outer top may not be higher than the top of its
containing block. When the float
occurs between two collapsing margins,
the float is positioned as if it had
an otherwise empty anonymous block
parent taking part in the flow. The
position of such a parent is defined
by the rules in the section on margin
collapsing.
The outer top of a floating box may not be higher than the outer top
of any block or floated box generated
by an element earlier in the source
document.
The outer top of an element's floating box may not be higher than
the top of any line-box containing a
box generated by an element earlier in
the source document.
A left-floating box that has another left-floating box to its left
may not have its right outer edge to
the right of its containing block's
right edge. (Loosely: a left float may
not stick out at the right edge,
unless it is already as far to the
left as possible.) An analogous rule
holds for right-floating elements.
A floating box must be placed as high as possible.
A left-floating box must be put as far to the left as possible, a
right-floating box as far to the right
as possible. A higher position is
preferred over one that is further to
the left/right.
It's because inline elements can't have a margin property. <label> is an inline element, and by floating it, you make it act as if it were an inline-block, allowing you to add a margin to it.
It's strange.
Try using display: inline-block; instead of float: left; and see what happens.
Sorry for my previous answer which I hope was deleted.
Margins are tricky. In this case, margins don't count against floats: they are computed from the place where the element would start if the float wasn't there. Possibly you can apply a margin-right to the float, or if you know the float's width add that plus its margin to the value you want to separate them.
A training made by the W3C consortium may help you.
And the specification with all the theory involved with this field: Visual formatting model