Should I Use More Than One CSS Sheet

Should I use more than one CSS sheet?

yes you should use more than one css file rather using one big file.
It helps you while maintaining your site also use different definitions (classe or id names) in different css otherwise it will take the one which declared later.
For example

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
   <html>
     <head>
        <link href="/stylesheets/stylesheet.css" media="screen" rel="stylesheet" type="text/css" />
        <link href="/stylesheets/lightbox_new.css" media="screen" rel="stylesheet" type="text/css" />
        <link href="/stylesheets/another_css.css" media="screen" rel="stylesheet" type="text/css" />
      </head>

      <body>
         <!-- Your content here -->
      </body>
  </html>

Single huge .css file vs. multiple smaller specific .css files?

A CSS compiler like Sass or LESS is a great way to go. That way you'll be able to deliver a single, minimised CSS file for the site (which will be far smaller and faster than a normal single CSS source file), while maintaining the nicest development environment, with everything neatly split into components.

Sass and LESS have the added advantage of variables, nesting and other ways to make CSS easier to write and maintain. Highly, highly recommended. I personally use Sass (SCSS syntax) now, but used LESS previously. Both are great, with similar benefits. Once you've written CSS with a compiler, it's unlikely you'd want to do without one.

http://lesscss.org

http://sass-lang.com

If you don't want to mess around with Ruby, this LESS compiler for Mac is great:

http://incident57.com/less/

Or you could use CodeKit (by the same guys):

http://incident57.com/codekit/

WinLess is a Windows GUI for comipiling LESS

http://winless.org/

Is it good idea to make separate CSS file for each HTML page?

Your example shows you using one design.css file for your entire website.

Generally, it is better to have one single .css file containing data for all pages for 2 reasons:

You will allow browsers to cache .css files thus resulting in faster loading times;
It will ease the maintenance process.

I would advise you, if you really want to divide .css in separate blocks to use CSS' @import to divide blocks of code f.e form styles and so on.

One big css file vs multiple small css files

There is pros and cons of both approaches.

Having multiple CSS files will allow you to organize and group your CSS files properly in development. However, this also means that there are multiple HTTP requests to make. HTTP requests are more expensive in terms of loading time as it has to contact the server and fetch the file.

Also once a file is loaded, it is cached by the browser. Which means, even-though it might be initially slower to load the huge.css, it doesn't need to be loaded again when you navigate around the site.

In my experience and adapted by most of the developers, you could do something like below to get most of the both worlds.

Use css pre-processers like SASS or LESS. Don't ask me which one is better, there is already enough arguments going around the web on that topic. Just pick one which you are comfortable with. My preference is SASS.

CSS pre-processers allows you to divide your CSS files into smaller more organized files. For example, you could have a main.sass which includes menu.sass, footer.sass, etc.

main.sass

include _menu
include _footer
include _header
...

_ tells sass not to compile seperate files for each of these sass files. So they all will only be compiled to a one main.css. These pre-processors come with a functionality to compile the given sass files into a css file that browser can read. You can also use tools like [livereload][4] to compile them in real-time.

You will have these sass files in your development code. But in your production code, you can simply use the compiled single css file.

If you are feeling more advantageous and want to take things further, you can use tool like Grunt or Gulp. They allow to automate your development tasks or build processes. So ideally, in development you could have a grunt task that watches all your sass files and automatically compiles them into the main.css file. In your index.html you can have reference to this main.css. Once you are happy, you can also have another task called build task, which can automatically compile all your css files and minimize them.

To clarify your question:

It depends what is best in case by case basis, what kind of site you have and how you have built it.

If you have a website where visitors are most likely to never navigate around the site than some particular pages, then its better to load css specific to that particular page and not combine it. You can load these css files in the partials specific to these page.

In my experience building many many sites,

its almost always best to load one combined css.
if a particular page requires css is not likely to be visited often, include a page specific css in its templete seperately with a conditional script tag.
Minimize all css files almost 100% of time

Also, I will suggest you to spend more time improving efficiency of your server side code or database, then worrying too much about the css. It will be more productive as most of the in-efficiency lies in server side.

How do you refer to more than one .css file in html?

Yes, just add the second bit as you mentioned:

<link rel="stylesheet" type="text/css" href="style12.css" />

Is it possible to have multiple css files for a single html file (to modularise the style sheets)

Yes, it is possible and also as simple as you pointed it out, just by simply adding each style into your html file. But keep in mind, using more style sheets is not the best way in order to keep up a good performance.

While rendering your html, your browser is only able of downloading 2 parallel files at a time. So using more than 1 css file would have negative effects on your performance. To avoid that I would recommend using more css files during development and using some tools like Grunt or Gulp to put all of your different css files together into 1 file.

One CSS file vs multiple for different pages

Advantages of one CSS file

Only one HTTP request is needed to fetch it, which improves the first page load time for most users and will speed up subsequent page loads, especially if users are expected to visit more than one different page type during their visit. This can also decrease server load.

Advantages of multiple CSS files

Reduces bandwidth, particularly if any given user is not likely to view many of the different page types on your site during their visit (which may be the case if your site is divided into almost completely unrelated sub-sites). Note that multiple CSS files will increase HTTP requests, which despite bandwidth savings may actually decrease load speed on modern connections.

I'm generally in favour of having a single CSS file for a site in most cases.

Is it good if I split my CSS file into multiple files for each page?

Ideally you want to abstracts your CSS files into many different SCSS files and then compiles them into one minified master file. One file for the header styling, one for links, one for typography. I was afraid of SCSS but now love it... Nothing changes in production, you are still running off CSS bit in development you are just making your life that little bit more organised.

Is is possible to embed 2 or more style sheets in one link tag?

No it's not possible to include multiple files in one <link> tag.

In your CSS-file, you can daisy-chain them into another file however using @import.

Lets say you have these files:

style.css
table.css
button.css

You can then in style.css do:

<!-- Including one css file into other -->
@import "table.css";
@import "button.css";

And in HTML import them all like this:

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

However you can use popular and powerful bundling tools such as Webpack that will bundle both your Javascript and CSS files.

Should I Use More Than One CSS Sheet