# Towards CSS

REMARKS

In this course section we prepare HTML files to apply (one or more) CSS layouts on them
- We link existing CSS files to HTML pages for different devices
We do not write our own CSS code (yet), "understanding" the code is enough for now

# Linking CSS files

Remember the (empty) <link/> tag that can be used in the <head> section to link a relevant resource (e.g. a favicon) to an HTML page

tag	description
<link/>	relevant resource

This <link/> tag will now be used for linking a CSS file to an HTML file
- As rel(ationship), we now specify "stylesheet"
- The href (hypertext reference) contains the place where the linked CSS file can be found
Emmet tip: link

...
<head>
    ...
    <link rel="stylesheet" href="style1.css">
</head>
...

1
2
3
4
5
6

# Example

The page is well structured and the document outline is clear:

example 1 outline

A CSS file (style1.css) is linked to the HTML page (index.html) so that the surfer also sees this logical structure
- The content of this CSS file is clear: the font and some color combinations are set
On a wide screen the readability of the text is poor (because the complete screen width is taken)

TIP

A (Code)Sandbox can be opened in a new browser window by selecting the 'Open in New Window' icon in the top right corner:
Open Sandbox in new browser window

We would like to limit the content width on wide screens to e.g. 800px to speed up the reading pace of the user
- Which tag can we use to realise this, taking into account that we still have 2 content tags (<div> and <span>) to discuss?

tag	description
<div>	block element
<span>	inline element

# Extra structure element <div>

Use a <div> tag to address a part of the page (that is not a <header>, <nav>, <main>, <article>, <section>, <aside>, <footer> or <figure>) for layout purposes
- Not used as often (as before), because you can use an alternative structure tag (<main>, <section>, ... ) in a lot of cases
Block element
Used to group a number of other block elements

# Example

Differences with previous example
- The whole content of the body is surrounded by <div> ... </div>
- An additional CSS file (style2.css) is linked to the HTML page index.html (AFTER the link to style1.css)
  - Contains some additional color combinations and extra code to limit the width of the <div>, center the <div> on the page, ...
The styles of the CSS files are applied in cascade (in series, in succession)
- The font is Verdana (only defined in style1.css)
- The <header> and <footer> are rendered in white text on a black background (the color choices for these elements defined in style2.css overrule those of style1.css)
- ...

# Extra structure element <span>

Use a <span> tag to address a part of text within a block element for layout purposes
Inline element
A <span> tag can only contain phrasing content, that is, content that can be inside a sentence (text, <img>, <a>, ...)

# Example

Differences with previous example
- The first word of the introduction and the five first words of the middle part are included in a <span> tag
- In style2.css extra CSS code is written to underline these <span> tags

# id and class

In the CSS code we have used so far, all tags (<header>, <footer>, <a>, <div>, <span>, ...) are styled in the same manner
- Exercise: Open the previous Sandbox and add a <div> tag with some lorem text (somewhere in the <body>) and observe the result!
If you want to use a specific style for (a) specific element(s), you will need the standard/common attributes id and class which can be attached to any HTML element

attribute	description
id	identifier; one
class	class; more than one

Naming conventions
- Case sensitive
- No spaces
- Must start with a letter

# id

Assigns a unique name to one HTML element
- A specific id can only occur once in a webpage
  - A webpage containing 2 elements with the same identifier is not valid/correct
  - In another webpage of the site an element with the same identifier is allowed
Usage
- As an anchor in (hyper)links (see A link to a specific point on a webpage)
- Style a specific HTML element with CSS (see below)
  - In CSS, we use # followed by the name of the id to select this specific HTML element
- Make web forms more accessible (see Full Stack Essentials)
- Access an HTML element in JavaScript/jQuery (see JavaScript)

# class

Can be attached to different HTML elements
- A specific class can occur multiple times in a webpage
Usage
- Style multiple elements (in the same way) with CSS (see below)
  - In CSS, we use . followed by the name of the class to select these multiple HTML elements
- Access (an) HTML element(s) in JavaScript/jQuery (see JavaScript)

REMARK

The difference between id and class can be remembered easily, as it resembles the organisation of the IT Factory
- Every student has a unique identifier, i.e. his/her student number. No other student has the same number.
- A class group consists of multiple students and students can take courses in different class groups

# Example

Differences with previous example
- Several identifiers (container, top) and classes (bold, underline) are added in index.html
- In style2.css, CSS code for these identifiers and classes is added
- <div id="container">...</div> (line 12)
  - The CSS code, originally written for all <div> tags, is moved to #container
  - As such, only this 'container' (the <div> with id="container") gets the specified layout (maximal width, centered, red border, ...)
- <h2 class="underline">Welcome!</h2> (line 31) and <span class="underline">Lorem ipsum dolor sit amet,</span> (line 47)
  - The styling specified in .underline (underline text) is applied to this heading <h2> and this <span>
- <span class="bold underline">dolor</span> (line 35)
  - The styling specified in .bold (bold text) and .underline (underline text) is applied to this <span>
  - Note that the value of the class attribute ("bold underline") equals both class names, separated by a space
- <a href="#" id="top" class="bold">top</a> (line 155)
  - The styling specified in .bold (bold text) and #top (capital letters) is applied to this link

REMARK

Use meaningful names for identifiers and classes, indicating the purpose of the corresponding code
- For example: class="warning" is a better choice than class="blue"

# Summary

HTML	CSS	remark
`<div id="id1">...</div>`	`#id1 {...}`	identifier: unique on webpage
`<span class="cl1 cl2">...</span>` `<a class="cl1">...</a>`	`.cl1 {...}` `.cl2 {...}`	class: allowed multiple times on webpage

# Media queries

# Different devices

If you study the print preview (of the last example), you notice that it's not printer-friendly: the red border is annoying, navigation links are useless on paper, ...

print preview

While linking a style sheet you can designate the device for which it is meant by adding the (optional) attribute media to the <link> tag
- Without a media attribute, the lay-out will be used on alle devices
- If you want to use the style sheet solely for a color monitor, this should be specified with media="screen"
- If you want to use the style sheet solely for printing, this should be specified with media="print"
  - Emmet-tip: link:print

media type	description
all	all devices
print	print preview/printer
screen	computers screens, tablets, smartphones, ...
speech	screenreaders

# Example

Differences with previous example
- The CSS files style1.css and style2.css are only used on monitors (media="screen" is added to their respective <link> tags):
  <link rel="stylesheet" href="style1.css" media="screen"/>
  <link rel="stylesheet" href="style2.css" media="screen"/>
- An extra CSS file style3.css is added, which will only be used for printing:
  <link rel="stylesheet" href="style3.css" media="screen"/>
  - Contains CSS code to hide the <header>, <nav> and <footer>
On a monitor, nothing changes
In the print preview, all styling (defined in style1.css and style2.css) and the information that's irrelevant on paper is gone

print preview 2

# Different screen sizes

On small screens the layout is far from perfect as quite some space is lost by the grey/red/white spacing around the text

mobile view

TIP

Go into developer mode (F12) and click the mobile icon to emulate the webpage on a mobile device
- Chrome:
- Firefox:

It's possible to include an additional test regarding the screen size in the media attribute, e.g., media="screen and (min-width: 600px)"

REMARK

Do not forget the brackets around the additional test: (min-width: 600px)

# Example

Differences with previous example
- The CSS file style2.css is only used on screens with a minimal width of 600px:
  <link rel="stylesheet" href="style2.css" media="screen and (min-width: 600px)"/>
- Different lay-out depending on the screen width

mobile view on small and large screens

TIP

Always work MOBILE FIRST: start by coding a basic layout for all screens, after which you specify what should be different on a wider screen

# Viewport

The attentive reader has observed that the HTML page index.html in this section contains the viewport <meta/> tag (line 5) in the <head> section
- The viewport refers to the area of the browser window in which content can be seen
- This <meta/> tag is extremely important when you want to code different layouts for different screen widths
  - Exercise: Comment the viewport <meta/> tag in the previous example and check what happens in mobile view (in the developer mode of your browser): the device does not report its actual screen width, and the style sheet style2.css is also applied on screens smaller than 600px
Emmet tip: meta:vp

WARNING

Do not forget to remove the unnecessary attributes (user-scalable, maximum-scale and minimum scale). More precisely,

<meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">

should become

<meta name="viewport" content="width=device-width, initial-scale=1.0">