CSS floating-float/clear text and detail

Tutorial Start:

The first thing to know is that P is a block-level element that has a single line in the page, arranged from top to bottom, which is the legendary stream . Such as:

As you can see, even if the width of the P1 is very small, the line in the page can tolerate P1 and p2,p2 and will not be ranked behind P1, because the P element is a exclusive line.

Note that these theories refer to p in the standard flow.

Side dishes think that, no matter how complex the layout, its basic starting point is: " how to display multiple p elements on one line."

It is clear that the standard flow has not been able to meet the demand, it will use floating.

floating can be understood as having a P The element is detached from the standard flow, floating above the standard stream, and the standard stream is not a hierarchy.

For example, assuming that the P2 floats, then it will be out of the standard flow, but P1, P3, P4 are still in the standard flow, so P3 will automatically move up, occupy the P2 position, and re-form a stream.

As can be seen, because of the P2 set floating, so it no longer belongs to the standard flow, P3 automatically up the displacement P2 position, p1, P3, P4 in order to become a new stream. And because the float is floating on the standard flow, so P2 block a part of the P3,P3 appears to be "short".

The P2 here is left-floating (float:left;), which can be understood as floating up, left-aligned, right-floating (float:right;) and, of course, on the right. Left and right are the left and right edges of the page.

If we use the P2 to float right, it will be as follows:

At this time P2 by the right edge of the page arrangement, no longer obscure P3, the reader can clearly see the above-mentioned P1, P3, p4 composition of the flow.

So far we've only floated one P element, many more?

Let's add the P2 and P3 to the left floating, the effect

Similarly, because P2, p3 float, they no longer belong to the standard flow, so P4 will automatically move up, and P1 form a "new" standard flow, and the float is floating on the standard flow , so P2 block P4.

Cough, to the point, when the P2, P3 set floating, P3 will follow P2, do not know if the reader has found, until now, p2 in each case is floating, but did not follow the P1. Therefore, we can draw an important conclusion:

if a P element a is floating, if a element is also floating on the previous element, a element will follow the previous element's after Edge ( If one row does not fit the two elements, the A element is squeezed to the next line) ; if a Element is an element in the standard flow, a the relative vertical position does not change, i.e. a The top of the line is always aligned with the bottom of the previous element .

The order of P is the HTML code in the P The order of the .

near the edge of the page is before , away from the edge of the page is after .

To help the reader understand, give a few more examples.

If we set P2, P3, P4 to the left float, the effect is as follows:

According to the above conclusion, with the side dish to understand again: first from P4 analysis, it found that the above element P3 is floating, so P4 will follow P3, P3 found that the above element P2 is also floating, so P3 will follow the P2, and P2 found that the upper element P1 is the element in the standard flow, So the relative vertical position of the P2 is constant, and the top is still aligned with the bottom of the P1 element. Because it is left floating, the left side is near the edge of the page, so the left side is front, so P2 is on the left.

If the P2, P3, P4 are set to the right floating, the effect is as follows:

The truth and left floating basically the same, just need to pay attention to the corresponding relationship. Because it is floating right, so the right side is near the edge of the page, so the right side is front, so P2 on the far right.

If we float the P2 and the P4 to the left, the following:

Still according to the conclusion, P2, P4 floating, out of the standard flow, so P3 will automatically move up, and P1 constitute a standard flow. P2 found that the previous element P1 is an element in the standard flow, so the P2 is not changed relative to the vertical position, aligned with the bottom of the P1. P4 found that the previous element p3 is the element in the standard flow, so the top of the P4 is aligned with the bottom of the P3, and is always true, as it can be seen that P3 moves up after the P4, and P4 always guarantees its top and last element P3 ( the bottom alignment of the elements in the standard stream.

At this point, congratulations to the reader has mastered the addition of floating, but there are clear floating, there is a basic clear floating on the top is very easy to understand.

Through the study above, it can be seen that: before the element floats, that is, in the standard flow, is vertical arrangement, and floating can be understood as a horizontal arrangement.

Clear float can be understood as breaking the horizontal arrangement.

The clear floating keyword is clear and the official definition is as follows:

Grammar:

Clear:none | Left | Right | Both

Value:

None: Default value. Allowed to have floating objects on both sides

Left: does not allow floating objects

Right: Do not allow floating objects

Both: Floating objects are not allowed

The definition is very easy to understand, but the reader may find that this is not the case when actually using it.

There is nothing wrong with the definition, but it is too vague to describe, which makes us overwhelmed.

According to the above basis, if there are only two elements in the page P1, p2, they are left floating, the scene is as follows:

At this time P1, p2 are floating, according to the rules, P2 will follow the P1 behind, but we still hope that P2 can be arranged under the P1, like P1 no float, p2 left floating.

This is the time to clear the float (clear), if only according to the official definition, the reader may try to write: in the P1 CSS style to add clear:right,, understood to not allow the P1 to the right of the floating element, because P2 is a floating element, it will automatically move down one line to satisfy the rule.

In fact, this understanding is not correct, this does not have any effect. See the side of the cake:

for CSS cleared float (clear) , be sure to keep in mind that this rule only affects the elements that use the purge itself, not other elements.

How do you understand it? Take the above example, we want to let P2 move, but we are using the P1 element of the CSS style to clear the float, trying to remove P1 to the right of the floating element (clear:right;) to force the P2 down, this is not feasible, because this clear float is called in the P1, It can only affect P1, can not affect P2.

According to the side of the cake, in order for P2 to move down, you have to use float in the P2 CSS style. In this example, the left side of P2 has a floating element P1, so as long as the clear:leftis used in the P2 CSS style, to specify that the P2 element is not allowed floating elements to the left, so P2 is forced to move down one line.

So if there are only two elements in the page P1, p2, are they all floating right? Readers should now be able to speculate on their own scenarios, as follows:

Now, if you want to move P2 down to P1, how do you do it?

Also based on the side-dish conclusion, we want to move the P2, we must call the float in the P2 CSS style, because the float only affects the element that invokes it.

You can see that there is a floating element on the right side of the P2 P1, then we can use Clear:right in the P2 CSS style, to specify that the right side of P2 does not allow floating elements, so P2 is forced to move down one line to the bottom of P1.