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書名： Practical Web Development
作者名： Paul Wellens
本章字數： 436字
更新時間： 2021-07-16 13:14:09

Adding styles to our documents

So how do the CSS rules become part of our document? There are three ways:

External style sheets
Internal CSS
Inline styles

External style sheets

This is the recommended way to add CSS to your site. It should be your goal for all style sheets of the production version of your site to be external. Simply add a line to the <head> section of your site, which should look like the following:

<link rel="stylesheet" type="text/css" href="css/style.css">

<link> is an HTML element we had not yet introduced. Its attributes are listed below:

rel, to indicate the relationship between the HTML document and the linked file.
type specifies the MIME type of the document so the browser knows how to load it.
href is used to specify the location of the file. You may expect a src attribute here, like is used for <img> tags, but the attribute to specify the file name in a <link> element is href. For the file name, we recommend that you always use relative pathnames. We suggest that you collect all your style sheets together in a folder with a meaningful name, like css or styles. Of course, the file itself should have a meaningful name too.

When the file does indeed exist, it will be loaded. That is why it is important that your <link> element resides in the <head> section of the document so all the CSS rules are read before the body of your document.

Internal CSS

For small projects, or projects you would like to limit to a single HTML file so that it is easy to email to someone, you can use internal CSS. All the CSS rules can then be placed inside the <head> section of your document, inside a <style> tag. That tag needs to, at a minimum, include a type attribute, as in the following example:

<style type="text/css">
p.red {
color:red;
}
</style>

Inline styles

Styles can be given to an inpidual HTML element by using the style attribute inside the HTML element itself, as in the following example:

<h3 style="color:green;">Congratulations</h3>

We do not recommend using this in your final product, but it is extremely useful to instantly see the effect of a change during development. If, for some reason, you leave one of the inline style attributes inside a page, it might take you forever to find out why your cool style sheet is not doing what it is supposed to be doing, on this one line of this one page.

On the other hand, I use it everyday, as I introduce and test new elements on a page while not disturbing anything else on the site, as modifying the external .css file would.

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Practical Web Development

Adding styles to our documents

External style sheets

Internal CSS

Inline styles