Is it valid to name divs like this?
<div class="frame header">Some content here</div>
With a space in the name? Then, of course, in the css I would have something like:
.frame { display: block; }
.header { background-color: #efefef; }
I guess I'm just wondering if you can have a space in the actual markup like I posted and it be XHTML strict? I've checked on the W3C validation, but for some reason, anything I put in there is passing. Sigh...
ids and classes can't have spaces. If you put a space then you're adding two classes, so W3 is interpreting that as it is and won't throw you an error. Your css is correct.
Yes, you can. The class is not really a 'name' for the element, but a list of classes that apply to it, separated by spaces. If you want that element to have a specific 'name' that pertains only to it, use the id attribute. Remember that is has to be completely unique in the document, and also that ID's cannot have spaces.
Something like:
<div class="frame" id="header">Some content here</div>
.frame { display: block; }
#header { background-color: #efefef; }
What you are doing is valid.
However, any number of <div> elements in an html/xhtml document can have the same class definitions for presentation purposes.
Since the name attribute has been replaced with id attribute in xhtml, it is always better to have an ID attribute to uniquely name and reference a particular element.
Related
I tried this:
input[time] {
margin: 2px;
}
...but it does nothing.
Just to see what, if anything would happen, I also added parring: 2px; but still nothing. So how can I get the time element to shove other elements that invade its personal space out of the way?
you need to specify it is a type like so
input[type="time"]{
margin: 2px;
}
This article goes other this further if you are interested,
Kieran
Use input[type="time"] instead of input[time]
The [attribute] CSS selector targets HTML tags who have a certain attribute no matter the attribute's value.
The [attribute="value"] CSS selector targets HTML tags with an attribute with a set value.
Here is the code I have a question about
.store {
display: block;
position: relative;
}
.store:before, .store:after {
display: block;
position:absolute;
content:'';
}
.store:before {
background: url(store-before.png);
height: 23px;
width: 54px;
top:-3px;
left:-3px;
}
.store:after {
background: url(store-after.png);
height: 20px;
width: 41px;
bottom:-3px;
right:-3px;
}
I noticed that when the "content" is anything besides two apostrophes, the before and after images don't show up. Can somebody explain the meaning of the two apostrophes? Thanks.
The Generated content, automatic numbering, and lists section of the CSS2.1 specification explains this:
Authors specify the style and location of generated content with the :before and :after pseudo-elements. As their names indicate, the :before and :after pseudo-elements specify the location of content before and after an element's document tree content. The 'content' property, in conjunction with these pseudo-elements, specifies what is inserted.
content is what is added to the page. If no content is specified, nothing is added to the page at all (meaning that ultimately no styling gets applied). content: '' adds empty string content to the page.
The two apostrophes denote a string. Two double quotes denote a string as well, which delimiter you use depends on preference and escaping needs; see here for all the details.
If there's nothing between the two string delimiters, either '' or "", then you have an empty string. If you have anything besides a string, it's some other value which may or may not be valid. See here for all the possible values for content. If you pass an invalid value, then like any other style declaration the browser will ignore it, and without any valid value content will default to normal, which is really none for the :before and :after pseudo-elements. That will prevent your pseudo-element from displaying.
To use the before and after elements, it needs to have some form of content before it will show the element, so you can use an empty string to pretend to be something there, obviously a space or empty will show nothing on the page, so you just get the rest of your css styling.
If you remove the content property then it wont show at all.
Its meant to be used for things like "..." or "read more" I imagine without having to have that in your html markup.
Your particular code snippet is probably using it for clearing.
How ever you can use it to put repeating content next to elements like so:
span:before{
content:"Author: "
}
<span>Huckleberry Finn</span>
Will result in:
Author: Huckleberry Finn
I was trying to put a image (logo) in the header element provided by HTML5 and I am curious if anyone knows if it is possible to declare a class in CSS something on the lines of header.image?
I tried header.image and it didn't seem to work, however as soon as I had the class named just .headerimage then it seem to be picking up the padding property I was trying to apply.
I'm doing some very basic learning as it's been sometime I picked up HTML code. Please help if your time permits. Thanks
I was trying to put a image (logo) in the header element provided by HTML5 and I am curious if anyone knows if it is possible to declare a class in CSS something on the lines of header.image?
I tried header.image and it didn't seem to work, however as soon as I had the class named just .headerimage then it seem to be picking up the padding property I was trying to apply.
I'm doing some very basic learning as it's been sometime I picked up HTML code. Please help if your time permits. Thanks
This is not the entire HTML/CSScode, but I could manage to take some screenshots. You guys helped me answer some questions and understand how period is not relevant to what I was trying to do.
Screenshot 1: https://skitch.com/android86/fm4r7/dreamweaver ( HTML design view) Screenshot 2: https://skitch.com/android86/fm4fd/dreamweaver ( CSS)
In the screenshot 1, I tried to have the links for website Contact and Login as a part of the Nav tag provided by html 5, however I wanted these to be horizontally next to the hgroup. I assigned a width to hgroup and now I have a lot of space to the right of hgroup however the nav is starting to line up horizontally, is this something I should handle with position or float property in CSS? I tried both in various combinations, I assigned a width to nav in order to fit in the area however it doesn't seems to be working. Any clue? The CSS code is in screenshot 2. After looking at the discussion here I thought using class might not be required instead rather parent child relation might be most relevant. I personally thought and read that one should use id's in CSS when it is a very unique scenario and class when we expect to use a certain thing very commonly, is this parent child relation a way of declaring a class? Thanks everyone.
In CSS, a period without spaces like this.thing means:
select elements that have the class thing but only if they are of type this
Period (.) is a special character in CSS, so you can't name classes with periods. Try an _ or a -.
Actually you can't use period in class names, because it is a class selector. For example, is you have a class "foo" applied to some html element, you can style this element in css linking to it as ".foo".
Example HTML:
<header class="foo">
<img class="bar" src="some/path/here">
Some content here
</header>
Example CSS:
.foo { color: #AAA; }
or
header.foo { color: #AAA; }
In first CSS example the style will be applyed to all elements, wich have class "foo". In the second - to all elements, wich have class "foo" and same time are of "header" type.
Returning to your case, I think the only aim is to apply style to image inside of header element. It can be done different ways:
Use the image class
.bar { width: 100px; }
or more concretely
img.bar { width: 100px; }
Use parent-child relations
header img { width: 100px; }
above will apply styles wich lay inside the header element or in its
children elements
header>img { width: 100px; }
this will be ok only for the direct child of header.
Combine two approaches.
If you know for shure that there will be only one image in header element, I can recommend the approach with ">". Read more about different css selectors, ids and classes. It will do the job.
Assuming your markup looks like this:
<header><img /></header>
The selector you want would be this:
header img {...}
If you really did class your image with class="image" (kinda redundant), then you'd want:
header .image {...} /* note space */
This assumes that the browser supports the html header element. If it doesn't, you'd want to use something like html5shim 1 or modernizer 2
I am a CSS newbie. I am just wondering, is that possible to include one common class into another class?
for example,
.center {align: center};
.content { include .center here};
I came across css framework - Blueprint. We need to put the position information into HTML, e.g.
<div class="span-4"><div class="span-24 last">
As such, we will place the positioning attribute inside html, instead of css. If we change the layout, we need to change html, instead of css.
That's the reason I ask this question. If I can include .span-4 into my own css, i won't have to specify it in my html tag.
Bizarrely, even though CSS talks about inheritance, classes can't "inherit" in this way. The best you can really do is this:
.center, .content { align: center; }
.content { /* ... */ }
Also I'd strongly suggest you not do "naked" class selectors like this. Use ID or tag in addition to class where possible:
div.center, div.content { align: center; }
div.content { /* ... */ }
I say this because if you do your selectors as broad as possible it ends up becoming unmanageable (in my experience) once you get large stylesheets. You end up with unintended selectors interacting with each other to the point where you create a new class (like .center2) because changing the original will affect all sorts of things you don't want.
In standard CSS, it's not possible to do this, though it would be nice.
For something like that you'd need to use SASS or similar, which "compiles" to CSS.
This is where the Cascading in Cascading Style Sheets comes in to play.
Think of your html element or widget/module (group of nested html elements) as an object. You know you're going to have objects that share the same properties so you'll want to create a reusable class they can utilize.
.baseModule {align: center;}
Say your module is a message (error, flash...). So you "extend" or "include" your .baseModule class because all messages will be center aligned (see final html example).
.message {border: 1px solid #555;}
Furthermore you want your error messages to have a red background. Additionally you can overwrite the border property from .baseModule.message here if you wanted it to be a different color or something.
.error {background-color: red;}
So now you have a few css definitions that can be reused with ease.
<!-- Regular message module -->
<p class="baseModule message">
I am a regular message.
</p>
<!-- Error message module -->
<p class="baseModule message error">
I am an error message. My background color is red.
</p>
To relate this to your question you'd basically leverage multiple class names for maximum reusability. Granted ie6 doesn't support chained selectors (class1.class2.class3), but it's still a neat trick!
In designing the HTML and CSS for a page, when should I use
img.className
versus
.className
versus
#idName
or some other variant?
Are there guidelines or recommendations?
Summary from answers
Thank you to all answerers - there is some excellent stuff here!
make CSS as specific as possible
use an OO approach
order: #id, tag, tag.className, .className
when to use each selector, also class/ID comparison
give selectors names based on purpose, not what they look like
use advanced selectors for smaller code, leave CSS classes for exceptions/overrides only
manage ASP.NET munging ID
In general you should be as specific as the item demands.
There is no general rule, it depends on the style in question.
A lot of people will recommend you keep to the lowest specificity with the theory that this allows the maximum cascading reuse but this is absolutely toxic in real world situations where you have multiple developers all working on slightly different versions of what a .foo might look like. Pollution from inheritance you did not want leads to massive bloat in trying to undo that locally or time-loss in refactoring.
The best guideline I always offer is to try and think of CSS in OO terms: class selectors map to interfaces more or less, tags map to classes, and ID selectors map to instances. Consequently decide if the style you want to apply really applies to that thing, all things like it, or anything which wants it.
I also strongly encourage you to make use of high level IDs on wrapper elements so you can write selectors in a namespace like fashion (i.e. #foo .bar, #foo .baz where #foo is unique to a page or set of page designs) which allows you both a level of specificity which reduces cross-design pollution and a level of generality which lets you make the most of cascading CSS reuse.
Best of both worlds.
It depends on the intended semantics, and, as others said, be as specific as possible.
#idName for unique elements on the page. Good examples are #header and #footer
TAGNAME for general purpose page styling.
TAG.classname and .classname for exceptions/overrides to the above rules.
And don't forget the use of advanced selectors. A bad example:
<style>
H1{ font-size: 200%; color: #008; }
#mainMenu { color: #800; }
.in_the_menu { color: #800; font-size: 150%; }
</style>
<h1>Hello World!</h1>
<div id="mainMenu">
<h1 class="in_the_menu">My Menu</h1>
</div>
The same could have been achieved with:
<style>
H1{ font-size: 200%; color: #008; }
#mainMenu { color: #800; }
#mainMenu H1 { color: #800; font-size: 150%; }
</style>
<h1>Hello World!</h1>
<div id="mainMenu">
<h1>My Menu</h1>
</div>
The second example gets rid of the superflous "class" attribute on the H1 element in the "mainMenu" div. This has two important benefits:
The HTML code is smaller and cleaner
You are less likely to forget to add the class attribute
If you take good care of you CSS, and make use of proper advanced selectors, you can nearly completely leave out CSS classes. And keep them only for exceptions/overrides.
Take this example which draws boxes with headers:
#content H2{
border: 1px solid #008789;
padding: 0em 1em;
margin: 0.2em 0em;
margin-bottom: 1em;
font-size: 100%;
background: #cccb79
}
#content H2 + DIV{
margin-top: -1em;
border-left: 1px solid #008789;
border-right: 1px solid #008789;
border-bottom: 1px solid #008789;
margin-bottom: 1em;
}
Now, as soon as you follow a H2 with a DIV in the #content element, you have a nice box. other DIVs and H2s are left alone:
<div id="content">
<h2>Hello Box!</h2>
<div>Some text</div>
<div>Some more text</div>
<div>Some more text</div>
<h2>And another title</h2>
</div>
If you get these rules right, you hardly ever need classes, and can work with IDs and TAG names alone. And as an added bonus, your HTML will be a lot nicer to read and maintain.
You preference should be, in order from highest to lowest:
id
tag
tag.className
.className
ID selectors are fast. Tag selectors are reasonably fast. Pure class selectors are slow because the browser essentially has to interrogate every element and see if each has that class. Getting elements by ID or tag name are "native" operations from a browser's context.
Also, I find it good practice to make your CSS selectors as restrictive as possible otherwise it just turns into a mess and you end up getting all sorts of unintended consequences where CSS rules apply where you didn't otherwise expect, which often forces you to create a similar yet different selector just so none of the rules regarding the first don't apply (translating into more mess).
Basically if you know if you only use a class on div elements then do this
div.className
not
.className
If you apply a class to several elements just list them:
h1.selected, h2.selected, h3.selected
instead of
.selected
In practice I find very few situations where you need to use "naked" class selectors or where it is advisable to do so.
you should use the selector best describing your rules
id: when you want to select one single element
.classname: when you want to style elements regardless of their tag
tag.classname: when you want to style only tags with the given class
tag tag tag: when you want to style all subelements of a tag
Class selectors
.className
This is to be used when you have more than one element on the page that you would like to apply the same style to. It can be to any tag element. So in the following all will use the same style as set out by the .className.
<p class="className"></p>
<img src="/path/to/image.png" class="className" />
But you can also restrict it like so:
img.className
By placing the tag along with the style definition, you're saying that this style is only to be used when it's the class used by that particular tag, in this case, an image.
HTML code will look like this:
<img src="/path/to/image.png" class="className" />
If you have other elements on the page using the same class style, but are not of the same tag, then the styles set out in this will not be applied and they will take on the more generic version as mentioned in the first example.
So repeating the example above:
<p class="className"></p>
<img src="/path/to/image.png" class="className" />
Only the image will take on the style as set out by img.className whereas all the rest will take on the style rules set in .className.
ID selectors
#idName
This is to be used when there is only one instance of a particular element that you wish to apply the style to.
You can also force it to apply only in certain tag conditions as you have earlier with the class definitions.
p#idName
This example will only apply to the paragraph block marked with the ID:
<p id="idName">
If you were to put that id on another element, like this:
<div id="idName"></div>
Then it will not take on the style set out and be ignored.
As to your two first selectors, the first of the two will overwrite the second, as it's more specific. You can calculate the specificity of a selector.
One thing worth noting is that some server side scripting technologies (most notably ASP.NET) don't play well with using IDs for your styling. If there is a chance your design will be used with such a technology, I recommend forgetting about #id selectors and use tag.className instead.
The reason is that ASP.NET actually changes the ID that ends up in the HTML based on a number of criteria, if the tag is output by a server side control.
I know this is a pretty old question but for all those who are reading this just now...
There are 4 categories of rules in general:
ID Rules, Class Rules, Tag Rules, Universal Rules.
And it's important to mention that class selectors are faster than tag selectors. So you should always use them in the following order
1. ID Selector
2. Class Selector
3. Tag Selector
4. Universal Selectors
In your case you should never use the tag name before class name.
You can find more information here: Writing efficient CSS
It really depends on the situation:
.error{
color:red;
}
p.error{
background-color:yellow;
}
div.error{
background-color:grey;
}
Always use the cascading effect of CSS to your advantage.
It's good practise to use the least specific rules you can for each rule.
How you structure your CSS will depend on the particular needs of the design.
Yes. You may want to use the same classname for two elements in the future. Be explicit and clear. This will also prevent class-rules from overlapping onto unintended elements.
h1.title { font-size:18px; } /* My h1's are big */
p.title { font-size:16px; } /* My p's are smaller */
.title { color:#336699; } /* All titles are blue */
Use ID's only when necessary, and only once per page.
When to use what depends on what you want to select. img.className (type selector + class selector) selects only IMG elements that’s in the class “className” while .className (just class selector) selects any element that’s in that class and #idName (id selector) any element with the ID “idName”.
But besides that, the selector all have a differente specificity that affects the order in which the properties of that rules overwrite the one of others.
So if you have an IMG element with the ID “idName” that’s in the class “className”:
<img src="…" id="idName" class="className">
The properties of the rules would be applied in the following order (specificity from highest to lowest):
#idName
img.className
.className
But when you use a specific class only for one specific type of elements (e.g. “className” only for IMG element), you can go with only .className.