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For this movie you can sit back and relax for a minute, it's not going to involve, actually has on exercises but is going to talk about where style comes from and the answer is not style fairies. It is in fact, a combination of three different sources. The one that you're probably most interested in is author styles, that's styles written by the author as in you. The second place that styles can come from, hopefully very rarely is from what we call user styles or reader styles. The person who is using a web browser can have their own style sheet associated with that web browser that's applied to every page that they view, every website that they visit every local document, every little XHTML document that they view, that's what a user style sheet is for. Very, very few people have these.
But it is still possible. There's a third source, which is absolutely common, no matter whether there's any other CSS involved or not, and that's the user agent styles, otherwise known as browser styles. This is a style behavior that's built into the web browser, and you might not think that there's the MRC spelt into the web browser, because after all, you might look at what you think of as an unstyled page. Here's an example of the Javaco site that we've been working with, with no styles, and I put no styles in quotes because actually there is a lot of styling going on in here.
The fact that there's a particular font in use, that unlinked text is black, link text is blue, images that are inside of links, like the Javaco tea have a border around them, that paragraphs sit apart from other elements and have some space above and below them, that headings do the same thing. That an h1 is big, bold and ugly this is all style information, it's all built into the browser the web browser has basically inherent in it a style sheet that says this is the absolute default for presenting an HTML or an XHTML document.
When you're an author style sheet, you're actually adding on top of that, you are adding your styles to the styles that are already built into the web browser. Because you might think that this an unstyle page actually, you can create an unstyled page by modifying some web browsers including Firefox. This is the same page, that's really unstyled. There's nothing being applied here by default, except for the hyperlink treatment. Well, the default colors in the default fonts because those are actually coming from the web browser's preferences and those are turned into style rules, but everything else you can see here that paragraphs don't really look like paragraphs anymore and headings don't look like headings, is all running together in one large undifferentiated mass of text. If you look down towards the bottom, just past the second image, it says post archive, July 2006, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, that's table markup, but I basically have taken away the browsers style sheet. it has no idea that it's supposed to treat the table in any sort of special way. It's just displaying that text like they are no elements at all. This is really unstyled and it could be even more unstyled, if we had a way of blocking the default font and the default colors and the default underlining of links. Like I said, that come from the browser preferences but it's still translated into CSS effects. So, it's a little scary, but I mean, that's life without styles and you couldn't actually sort of hack your browser to do this and then go browsing around the web.
It's difficult, but it can be done. So that's one source of style, is the user agent styles, the browser styles, they are built in and that's the basis, that's the lowest sort of level of style, it's the foundation. That's the first potential source of style. The second one, which we mentioned before, is user styles reader styles. In any case where the reader styles conflict with the user agent styles the reader styles are going to win. In considering the source, this is sort of the first step in the cascade, in the conflict resolution built into the cascade. The browser says okay if I have user styles, those are going to win out over the user agent styles, all other things being equal.
The reason that there are reader styles, or user styles is for accessibility purposes, these are here for people who really need them. So, assume that I am a user who is completely color blind, absolutely cannot perceive any colors, the entire world is grayscale to me. In that case I can't distinguish necessarily between blue text and black text, to tell which are hyperlinks and which are not and so I might decide that I always want my links to be underlined, absolutely no matter what. Ok, so I can set up my user style sheet, to say that links must always be underlined and do not let anyone else overwrite that and apply that to all pages that I visit, or making sure I always underline all my links, maybe I want all of my texts always be black on white, but I want all of my links to be in reverse text, white text on a black background. These are just the various possibilities, reasons why a user might want to create their own style sheet. The truth of the matter is that even those people who would really benefit from user style sheets don't realize they're there, in the same way that almost nobody ever realizes that they can change their default fonts or their default font sizes, even people who are blind or colorblind or otherwise have reasons so they might want to use a user style sheet don't know that it's there.
However, the people who do know that a user style sheet is there and make use of it, if you somehow manage to override what they've done you will hear from them. So, it's something to keep in mind there. So, like I say, user style sheets are very rarely encountered. Far more common are author style sheets. The thing that you write in creating the layout of a page and setting colors and fonts and all that kind of fun stuff. So there will inevitably be conflicts between these three things. If you as the author say that you want your unvisited links to the green, the web browser has user agent styles, that say that unvisited links should be blue. That's a conflict, one of the two has to win and the cascade is how they are resolved, and the first step of that is to consider the sources and say okay, if an author style conflicts with the user agent style the author style wins.
The step after that considers specificity, which is the subject of the next movie.
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