跳至主要内容

[CSS] Basics

CSS stands for "Cascading Style Sheets"

Selector {
  property: value;
}

Adding CSS​

Three ways to add CSS:

External CSS​

Use <link> tag (in the <head> section)

<head>
  <title>My first CSS website!</title>
  <link rel="stylesheet" type="text/css" href="style.css" />
</head>
  • rel - relationship: stylesheet
  • type - media type: text/css
  • href - Hypertext REFerence: style.css (file path)

Internal CSS​

The internal style is defined inside the <style> element(in the <head> section)

<head>
  <title>My first CSS website!</title>
  <style>
    li {
      background-color: green;
    }
  </style>
</head>

Inline CSS​

Add the style attribute to the relevant element: style="" (inside an HTML element)

<h1 style="color:blue;text-align:center;">This is a heading</h1>
資訊

The value from the last read style sheet will be used. So an inline style has the highest priority, and will override external and internal styles and browser defaults. Ref. How to add CSS (w3schools.com)

Cascading Order​

CSS Syntax​

CSS syntax

  • Selector: the selector points to the HTML element you want to style.
  • Declaration block: the declaration block within {} contains one or more declarations separated by semicolons: {Property1: Value1; Property2: Value2}

CSS Properties​

資訊

CSS Selectors​

5 categories of CSS selectors

1. Simple selectors​

Select elements based on name, id, class.

  • HTML tag: such as h1, div...etc.
  • .class: select a group of elements
    • element.class: select only specific HTML elements with the class
    • <p class="center large">: an element can have more than one class
  • #id : unique (should prevent using id)
  • *: all elemnets

2. Combinator selectors​

Combinator selectors

Select elements based on a specific relationship between them.

  • element, element - (,)
  • element element - descendant selector (space)
  • element > element - child selector (>)
  • element + element - adjacent sibling selector (+)
  • element ~ element - general sibling selector (~)

3. Pseudo-class selectors​

Pseudo-class selectors

Select elements based on a certain state: to define a special state of an element.

  • Anchor Pseudo-classes
    • element:link
    • element:visited
    • element:hover
    • element:active
  • :first-child Pseudo-class
  • :last-child Pseudo-class

4. Pseudo-elements selectors​

Pseudo-elements selectors

Select and style a part of an element.

5. Attribute selectors​

Attribute selectors

Select elements based on an attribute or attribute value.

資訊

CSS Comments​

/* This is a single-line comment */

CSS borders​

Border - Shorthand Property

The border property is a shorthand property for the following individual border properties:

  • border-width
  • border-style (required)
  • border-color

Icons​

Icon libraries:

Font Awesome​

To use the Font Awesome icons, go to fontawesome.com, sign in, and get a code to add in the <head> section of your HTML page:

<script
  src="https://kit.fontawesome.com/*yourcode*.js"
  crossorigin="anonymous"
></script>

Read more about how to get started with Font Awesome in our Font Awesome 5 tutorial.

Google Icons​

To use the Google icons, add the following line inside the <head> section of your HTML page:<link rel="stylesheet" href="https://fonts.googleapis.com/icon?family=Material+Icons">

<!doctype html>
<html>
  <head>
    <link
      rel="stylesheet"
      href="https://fonts.googleapis.com/icon?family=Material+Icons"
    />
  </head>
  <body>
    <i class="material-icons">cloud</i>
    <i class="material-icons">favorite</i>
    <i class="material-icons">attachment</i>
    <i class="material-icons">computer</i>
    <i class="material-icons">traffic</i>
  </body>
</html>
  • a:link - a normal, unvisited link
  • a:visited - a link the user has visited
  • a:hover - a link when the user mouses over it
  • a:active - a link the moment it is clicked

When setting the style for several link states, there are some order rules:

  • a:hover MUST come after a:link and a:visited
  • a:active MUST come after a:hover

Lists​

Block vs Inline Elemenets​

Block-level Elements​

A block-level element always starts on a new line and takes up the full width available (stretches out to the left and right as far as it can).

Examples of block-level elements

  • <div>
  • <h1> - <h6>
  • <p>
  • <form>
  • <header>
  • <footer>
  • <section>

Inline Elements​

An inline element does not start on a new line and only takes up as much width as necessary.

Examples of inline elements

  • <span>
  • <a>
  • <img>

Display​

display: none;​

display: none; is commonly used with JavaScript to hide and show elements without deleting and recreating them. The element will be hidden, and the page will be displayed as if the element is not there.

  • The <script> element uses display: none; as default.
  • visibility:hidden; also hides an element. However, the element will still take up the same space as before. The element will be hidden, but still affect the layout:

display: flex;​

CSS Transitions & Transforms​

Ref. https://thoughtbot.com/blog/transitions-and-transforms