While specifying a percentage value in css calc, how does calc know whether I am referring to width or height?
.container {
width: calc(100% - 2vw); // 100% here is width or height ?
}
One may assume that it is either width or height depending on the property you are accessing, (width in this case). If that were the case, what happens if you would like to do some calculation based on a different property? For instance, set the width based on some calculation of height? Say, set the container width to be 1.5 times height?
From the specification
The computed value of a calc() expression is the expression with all components computed.
Where percentages are not resolved at computed-value time, they are not resolved in calc() expressions, e.g. calc(100% - 100% + 1em) resolves to calc(1em + 0%), not to 1em. If there are special rules for computing percentages in a value (e.g. the height property), they apply whenever a calc() expression contains percentages.
There is no magic when using percentage inside calc() they will simply behave as if you aren't using calc().
So using width:100% is exactly the same as width:calc(100%) which is also the same as calc(50% + 50%). when you add another unit like width:calc(100% - 2em) it's like calculating width:100% then you remove 2em from it.
Basically, calc() is useful when combining percentage and non-percentage value in order to have accurate and precise result like removing 10px from 50% of the total width by using width:calc(50% - 10px).
what happens if you would like to do some calculation based on a different property? For instance, set the width based on some calculation of height?
You cannot do such thing with calc(). CSS in general doesn't allow such thing. You can either consider JS, some hacks to preserve ratio between width/height or use CSS variable and assign the same value for different properties.
Related question where the use of calc() combined with CSS variable is missused: Calc() outputting unexpected value
To answer the second part of the question:
For instance, set the width based on some calculation of height? Say, set the container width to be 1.5 times height?
You can do this with the aspect-ratio property:
.container {
text-align: center;
height: 200px;
/* width / height ratio */
aspect-ratio: 1 / 1.5;
background: lightgray;
}
<div class="container">
some content
</div>
Related
I'm trying to make a website where the maximum width is 500px, but if the window size is smaller (e.g. the user is on mobile, etc.), I want the width to just be 90%. How do I make it find the smaller value between 500px and 90%? This is what I've tried:
element {
width: 90%, 500px;
}
What am I doing wrong?
You can use width:min...
The min() CSS function lets you set the smallest (most negative) value from a list of comma-separated expressions as the value of a CSS property value.
MDN
div {
height:50px;
background: red;
width: min(90%, 500px);
}
<div></div>
Codepen Demo
I'm not a coder (which will soon become apparent) but I'm working on something for a work project and I'm stuck on the final bit.
I need to add a calc() working into the scale but it just won't work. Without going in to the in's and outs of why I need this, I know generally there would be better ways of doing what I want to achieve but I just want to know how I can get this working the way I need it.
I want the Transform: Scale() to adapt in size relative to the viewport size. I would assume from my research I add a calc() function using 100vw and my other workings.
I've put where I am so far below the scale function works as should i.e indivual values from 0-1 change the scale up to 100%. The Calc() function works fine with basic sums i.e 10 - 5 gives a value of 5 and 500% zoom but as soon as I add 100VW it stops working please please help!
body {
margin: 0;
padding: 0;
width: 100vw;
text-align: center;
}
#wrap {
width: 1535;
height: 900;
padding: 0;
overflow: hidden;
}
#frame {
width: 1535;
height: 900;
overflow: hidden;
-webkit-transform: scale(calc(100vw/1535));
-webkit-transform-origin: 0 0;
}
Two things here.
Your #wrap and #frame need to have some kind of unit on their widths. So this is your chance to change sizes relative to the viewport. For example, if you want them to be 1535px wide when the viewport is 1920px wide, but you want them to maintain that ratio as the viewport shrinks, set them to be 79.947917vw wide. (1535 / 1920 = 0.79947917). You can do something similar with the heights as well.
A scale transformation doesn't need units. Scales take a unitless number, which serves as a multiple of the element's original size. So scale(2) is twice as large as normal, or scale(0.5) is half as large as normal. You can also use two numbers to adjust the element's width and height differently. For example, scale(2, 3) would make the element grow to twice its original width and three times its original height.
Since transforms are relative to the element and not to the document, this means that you don't need to use any kind of calc inside your transform expression because having the element itself shrink and grow as the viewport shrinks and grows will also cause the amount of scaling to shrink and grow proportionally as well.
If you look at the CSS box model spec, you'll observe the following:
The [margin] percentage is calculated with respect to the width of the generated box's containing block. Note that this is true for 'margin-top' and 'margin-bottom' as well. If the containing block's width depends on this element, then the resulting layout is undefined in CSS 2.1. (emphasis mine)
This is indeed true. But why? What on earth would compel anyone to design it this way? It's easy to think of scenarios where you want, e.g. a certain thing to always be 25% down from the top of the page, but it's hard to come up with any reason why you would want vertical padding to be relative to the horizontal size of the parent.
Here's an example of the phenomenon I'm referring to:
<div style="border: 1px solid red; margin: 0; padding: 0; width: 200px; height: 800px;">
This div is 200x800.
<div style="border: 1px solid blue; margin: 10% 0 0 10%;">
This div has top-margin of 10% and left-margin of 10% with respect to its parent.
</div>
</div>
http://jsfiddle.net/8JDYD/
Transferring my comment to an answer, because it makes logical sense. However, please note that this is unfounded conjecture. The actual reasoning of why the spec is written this way is still, technically, unknown.
Element height is defined by the height of the
children. If an element has padding-top: 10% (relative to parent
height), that is going to affect the height of the parent. Since the
height of the child is dependent on the height of the parent, and the
height of the parent is dependent on the height of the child, we'll
either have inaccurate height, or an infinite loop. Sure, this only
affects the case where offset parent === parent, but still. It's an
odd case that is difficult to resolve.
Update: The last couple sentences may not be entirely accurate. The height of the leaf element (child with no children) has an effect on the height of all elements above it, so this affects many different situations.
For "n%" margin (and padding) to be the same for margin-top/margin-right/margin-bottom/margin-left, all four have to be relative to the same base. If top/bottom used a different base than left/right', then "n%" margin (and padding) wouldn't mean the same thing on all four sides.
(Also note having the top/bottom margin relative to the width enables a weird CSS hack that allows you to specify a box with an unchanging aspect ratio ...even if the box is rescaled.)
I vote for the answer from #ChuckKollars after playing with this JSFiddle (on Chrome 46.0.2490.86) and referring to this post (written in Chinese).
A major reason against the infinite calculation conjecture is that: using width faces the same infinite calculation problem.
Have a look at this JSFiddle, the parent display is inline-block, which is eligible to define margin/padding on it. The child has margin value 20%. If we follow the infinite calculation conjecture:
The width of the child depends on the parent
The width of the parent depends on the child
But as a result, Chrome stops the calculation somewhere, resulting:
If you try to expand the "result" panel horizontally on the JSFiddle, you will find that the width of them will not change. Please note that the content in the child is wrapped into two lines (not, say, one line), why? I guess Chrome just hard-code it somewhere. If you edit the child content to make it more (JSFiddle), you will find that as long as there is extra space horizontally, Chrome keeps the content two lines.
So we can see: there is some way to prevent the infinite calculation.
I agree with the conjecture that: this design is just to keep the four margin/padding values based on the same measure.
this post (written in Chinese) also proposes another reason is that: it is because of the orientation of reading/typeset. We read from top to down, with the width fixed and height infinite (virtually).
I realize the OP is asking why the CSS specification defines top/bottom margin percentages as a % of width (and not, as would be assumed, height), but I thought it might also be useful to post a potential solution.
Most modern browsers support vw and vh now which lets you specify margin numbers against the viewport width and viewport height.
100vw/100vh equals 100% width/100% height (respectively) if there's no scrollbar; if there is a scrollbar the viewport numbers don't account for this (while the % numbers do). Thankfully, nearly all browsers use scrollbar sizes of 17px (see here), so you can use css calc function to account for this. If you don't know whether a scrollbar will appear or not, then this solution will not work.
For example: Assuming no horizontal scrollbar, a top margin of 50% of height, could be defined as "margin-top: 50vh;". With a horizontal scrollbar, this could be defined as "margin-top: calc(0.5 * (100vh - 17px));" (remember that the minus and plus operators in calc require spaces on both sides!).
I know this question is a bit old, but I'd like to refresh it for CSS3. While it's true that the CSS2.1 specification says that percentage padding and margin are defined relative to the width of the containing block, this is not always the case. It depends on the writing mode. This comes straight from the CSS3 specs:
As a corollary, percentages on the margin and padding properties, which are always calculated with respect to the containing block width in CSS2.1, are calculated with respect to the inline size of the containing block in CSS3.
I cover this in my tutorial on aspect ratios with CSS.
Specifically, there's a section on Percentage Padding in Horizontal vs. Vertical Writing Modes. By default, an element has a horizontal writing mode, where text flows horizontally (in the "inline" direction) from left to right. However, using the writing-mode CSS property, you can actually set the mode to be vertical (with text either flowing from right to left or left to right). Here are some diagrams of horizontal vs vertical writing modes:
These are taken from the MDN docs on writing modes.
In vertical writing modes, percentage padding will be relative to the height of the containing block, not to the width.
Here's proof:
.document {
writing-mode: vertical-rl;
width: 100%;
height: 100vh;
}
.parent {
width: 100%;
height: 200px;
background-color: black;
color: white;
}
.child {
padding: 10%;
background-color: white;
color: black;
border: solid 1px;
}
<div class="document">
<div class="parent">
<div class="child">
Child
</div>
</div>
</div>
The child gets 20px of padding, which is 10% of its containing block's height (200px).
As to the why in the question, this was covered well in the other posts here.
Why don't we have box-sizing: margin-box;? Usually when we put box-sizing: border-box; in our style sheets we really mean the former.
Example:
Let's say I have a 2 column page layout. Both columns have a width of 50%, but they look kind of ugly because there's no gutter (gap in the middle); Below is the CSS:
.col2 {
width: 50%;
float: left;
}
To apply a gutter you might think we could just set a right margin on the first of the 2 columns; something like this:
.col2:first-child {
margin-right: 24px;
}
But this would make the second column wrap onto a new line, because the following is true:
50% + 50% + 24px > 100%
box-sizing: margin-box; would solve this issue by including margin in the calculated width of the element. I would find this very useful if not more useful than box-sizing: border-box;.
Couldn't you use width: calc(50% - 24px); for your cols? Then set your margins.
I think we could have a box-sizing: margin-box. The css box model shows exactly, what are the positions of the margins of the frames.
There are minor problems - for example, the margin boxes can overlap - but they aren't hard to solve.
I think, the situation is the same, as we can see with the overflow-x & overflow-y combinations, with the absolut positionied divs in table-cells, with the combination of min|max-width|height with the box-sizing, and so on.
There are features, really simple features, which the browser developers simply doesn't develop.
IMHO, box-sizing: margin-box were a very useful feature. Another useful feature were the box-sizing: padding-box, it exists at least in the standard, but it wasn't implemented in any of the major browsers. Not even in the newest chrome!
Note: #Oriol 's comment: Firefox did implement box-sizing: padding-box. But others didn't, and it was removed from the spec. Firefox will remove it in version 50. Sad.
The guy at the top is asking about adding margin to the overall width, including padding and border. The thing is, margin is applied outside the box and padding and border aren't, when using border-box.
I have tried to achieve the border-margin idea. What I have found is that if using margin you can either add a class of .last to the last item (with margin, then apply a margin of zero, or use :last-child/:last-of-type). Or add equal margins all the way around (similar to the padding version above).
See examples here: http://codepen.io/mofeenster/pen/Anidc
border-box calculates the width of the element + its padding + its border as the total width. So if you have 2 divs which are 50% wide, they will be adjacent. If you add 8px padding to them, then you will have a gutter of 16px. Combine that with a wrapping element - which also has padding of 8px - you will have a nicely laid out grid with equal gutters all the way around.
See this example here: http://codepen.io/mofeenster/pen/vGgje
The latter is my favourite method.
I'm sure all of this is obvious, but I'll type it out anyway because...well, I need the exercise. Would the following outcome not be just as efficient as box-sizing: margin-box;:
.col2 {
width: 45%;
height: 90%;
margin: 5% 2.5%;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
float: left;
}
http://jsfiddle.net/Fg3hg/
box-sizing is used to control from which point the padding and border are assessed to the overall size of the element. So while it's not kosher to include px margins with a % width (as is usually always the case), it's easier to calculate what the relative percentage amount should be because you don't have to incorporate padding and borders to the defined width.
This is because the box-sizing attribute refers to the size of an element after computing the given dimension-specific values (padding, borders). "box-sizing: border-box" sets the height/width of an element and takes into consideration the padding as well as the border width. The scope of an element's margin is greater than the element itself, meaning it modifies the flow of the page and its surrounding elements, therefore directly altering the way the element fits within its parent relative to its sibling elements. Ultimately a "margin-box" attribute value would cause major problems and is essentially the same as setting the elements height/width directly.
Dimensions of block-level, non-replaced elements in normal flow must satisfy
margin-left + border-left-width + padding-left + width + padding-right + border-right-width + margin-right = width of containing block
When over-constrained, browsers must adjust either the left or right margin.
I think that means the width of the margin box must equal the width of the containing block (i.e. 100%).
For your case, transparent borders with box-sizing: border-box can work much like margins.
On Codrops there are a couple of good articles on the subject of the effect of margins and row's forced to overflow. They suggest using the rem or em unit with a normalizer css setting font size to 100% for all browsers, then when you set widths and margins it is easy to keep track of the effect on the row's width by simply making a note in comments for the total width. A conversion of 16px to 1 em is the way to calculte the targeted viewports total witdh.
Working like that for the dev stage at least and then if you want 'responsive' templates you can convert widths to % including the margin widths.
The other and often simpler way they suggest to handle gutters is to use the pseudo after and the content: ''; on each of your columns which I find works really well. If you set a div class that is the defined last column such as end you can then target that class not to have the pseudo after, or to have a wider one; which ever best suits your layout.
The added bonus of using this pseudo element method is it also gives you a target for shadows that can give a more 3d effect and greater depth to the flat image on the readers monitor as well. I am experimenting with this effect at the moment by scaling up the effects being used on buttons, 'tweaking' the gradients, and the z-index.
Perhaps set the border to 0% opacity using RGBA and use the border as a margin.
There interesting situation when using box-sizing inside body content
no content no border box gives no any value on left-right margin % recount of this two box recount algoritms
.body{
box-sizing: border-box;
margin:0 3%;
}
Firefox versions before 57 also supported the padding-box value for
box-sizing, though this value was been removed from the specification
and later versions of the browser.
So margin-box even not planned...
There should be a box-sizing: margin-box;
But does the following work:
Put a div around it with
.divX{
width: XX%;
display:flex;
align-items: center;
justify-content: center;
}
How one could create a CSS rule for width which
Uses 100% width by default
If 100% width exceeds certain pixel width (let's say 512 px), then the width is clamped down to this pixel width
I am not sure about width and max-width relations, or how calc() is supported or could express this. This would need to work with the latest WebKit browsers and Firefox 4. IE8 etc. support not needed
That's in fact the intended use of max-width. If the computed (actual) width of an element exceeds max-width, it will be constrained to the max value instead of going beyond it. Percentage versus pixels isn't relevant.
Declare both in the same rule like this (no need for the calc() function):
#somediv {
width: 100%;
max-width: 512px;
}
If it's block level element it should be 100% by default so no need to declare the width, then max-width: 512px; would curtail it
calc() is not supported very well at all, but in this case I wouldn't think you would need it
div{ max-width: 512px; }
should suffice.