Key Concepts

Review core concepts you need to learn to master this subject

Link Element <link>

Purpose of CSS

Class and ID Selectors

Write CSS in Separate Files

Groups of CSS Selectors

Write CSS in HTML File

Selector Chaining

!important Rule

See more

Link Element <link>

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The <link> element is used to link HTML documents to external resources like CSS files. It commonly uses:

  • href attribute to specify the URL to the external resource
  • rel attribute to specify the relationship of the linked document to the current document
  • type attribute to define the type of content being linked

Purpose of CSS

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS, or Cascading Style Sheets, is a language that is used in combination with HTML that customizes how HTML elements will appear. CSS can define styles and change the layout and design of a sheet.

Class and ID Selectors

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS classes can be reusable and applied to many elements. Class selectors are denoted with a period . followed by the class name. CSS ID selectors should be unique and used to style only a single element. ID selectors are denoted with a hash sign # followed by the id name.

Write CSS in Separate Files

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS code can be written in its own files to keep it separate from the HTML code. The extension for CSS files is .css. These can be linked to an HTML file using a <link> tag in the <head> section.

Groups of CSS Selectors

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

Match multiple selectors to the same CSS rule, using a comma-separated list. In this example, the text for both h1 and h2 is set to red.

Write CSS in HTML File

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS code can be written in an HTML file by enclosing the code in <style> tags. Code surrounded by <style> tags will be interpreted as CSS syntax.

Selector Chaining

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS selectors define the set of elements to which a CSS rule set applies. For instance, to select all <p> elements, the p selector can be used to create style rules.

!important Rule

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The CSS !important rule is used on declarations to override any other declarations for a property and ignore selector specificity. !important rules will ensure that a specific declaration always applies to the matched elements. However, generally it is good to avoid using !important as bad practice.

Chaining Selectors

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS selectors can be chained so that rule sets apply only to elements that match all criteria. For instance, to select <h3> elements that also have the section-heading class, the selector h3.section-heading can be used.

CSS Type Selectors

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS type selectors are used to match all elements of a given type or tag name. Unlike for HTML syntax, we do not include the angle brackets when using type selectors for tag names. When using type selectors, elements are matched regardless of their nesting level in the HTML.

CSS class selectors

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The CSS class selector matches elements based on the contents of their class attribute. For selecting elements having calendar-cell as the value of the class attribute, a . needs to be prepended.

HTML attributes with multiple values

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

Some HTML attributes can have multiple attribute values. Multiple attribute values are separated by a space between each attribute.

Inline Styles

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

CSS styles can be directly added to HTML elements by using the style attribute in the element’s opening tag. Each style declaration is ended with a semicolon. Styles added in this manner are known as inline styles.

Selector Specificity

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

Specificity is a ranking system that is used when there are multiple conflicting property values that point to the same element. When determining which rule to apply, the selector with the highest specificity wins out. The most specific selector type is the ID selector, followed by class selectors, followed by type selectors. In this example, only color: blue will be implemented as it has an ID selector whereas color: red has a type selector.

Separating HTML code from CSS code

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

It is common practice to separate content code in HTML files from styling code in CSS files. This can help make the code easier to maintain, by keeping the syntax for each file separate, and any changes to the content or styling can be made in their respective files.

CSS ID selectors

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The CSS ID selector matches elements based on the contents of their id attribute. The values of id attribute should be unique in the entire DOM. For selecting the element having job-title as the value of the id attribute, a # needs to be prepended.

CSS descendant selector

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The CSS descendant selector combinator is used to match elements that are descended from another matched selector. They are denoted by a single space between each selector and the descended selector. All matching elements are selected regardless of the nesting level in the HTML.

CSS declarations

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

In CSS, a declaration is the key-value pair of a CSS property and its value. CSS declarations are used to set style properties and construct rules to apply to individual or groups of elements. The property name and value are separated by a colon, and the entire declaration must be terminated by a semi-colon.

Font Size

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The font-size CSS property is used to set text sizes. Font size values can be many different units or types such as pixels.

Background Color

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The background-color CSS property controls the background color of elements.

Opacity

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The opacity CSS property can be used to control the transparency of an element. The value of this property ranges from 0 (transparent) to 1 (opaque).

Font Weight

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The font-weight CSS property can be used to set the weight (boldness) of text. The provided value can be a keyword such as bold or normal.

Text Align

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The text-align CSS property can be used to set the text alignment of inline contents. This property can be set to these values: left, right, or center.

CSS Rule Sets

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

A CSS rule set contains one or more selectors and one or more declarations. The selector(s), which in this example is h1, points to an HTML element. The declaration(s), which in this example are color: blue and text-align: center style the element with a property and value. The rule set is the main building block of a CSS sheet.

Setting foreground text color in CSS

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

Using the color property, foreground text color of an element can be set in CSS. The value can be a valid color name supported in CSS like green or blue. Also, 3 digit or 6 digit color code like #22f or #2a2aff can be used to set the color.

Resource URLs

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

In CSS, the url() function is used to wrap resource URLs. These can be applied to several properties such as the background-image.

Background Image

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The background-image CSS property sets the background image of an element. An image URL should be provided in the syntax url("moon.jpg") as the value of the property.

Font Family

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

The font-family CSS property is used to specify the typeface in a rule set. Fonts must be available to the browser to display correctly, either on the computer or linked as a web font. If a font value is not available, browsers will display their default font. When using a multi-word font name, it is best practice to wrap them in quotes.

Color Name Keywords

<!-- How to link an external stylesheet with href, rel, and type attributes --> <link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css">

Color name keywords can be used to set color property values for elements in CSS.

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CSS Setup and Selectors
Lesson 1 of 2
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  1. 1
    The basic structure of every web page, HTML, is very plain on its own. The beautiful websites that you see across the internet are styled with a variety of tools, including CSS. CSS, or Cascad…
  2. 2
    Although CSS is a different language than HTML, it’s possible to write CSS code directly within HTML code using inline styles. To style an HTML element, you can add the style attribute directly…
  3. 3
    Inline styles are a fast way of styling HTML, but they also have limitations. If you wanted to style, for example, multiple elements, you would have to add inline styling to each element manually…
  4. 4
    Developers avoid mixing code by storing HTML and CSS code in separate files (HTML files contain only HTML code, and CSS files contain only CSS code). You can create a CSS file by using the **.css…
  5. 5
    Perfect! We successfully separated structure (HTML) from styling (CSS), but the web page still looks bland. Why? When HTML and CSS code are in separate files, the files must be linked. Otherwise,…
  6. 6
    CSS can select HTML elements by using an element’s tag name. A tag name is the word (or character) between HTML angle brackets. For example, in HTML, the tag for a paragraph element is . The CSS …
  7. 7
    CSS is not limited to selecting elements by tag name. HTML elements can have more than just a tag name; they can also have attributes. One common attribute is the class attribute. It’s also possi…
  8. 8
    We can use CSS to select an HTML element’s class attribute by name. So far, we’ve selected elements using only one class name per element. If every HTML element had a single class, all the style …
  9. 9
    If an HTML element needs to be styled uniquely (no matter what classes are applied to the element), we can add an ID to the element. To add an ID to an element, the element needs an id attribute: …
  10. 10
    CSS can select HTML elements by their tag, class, and ID. CSS classes and IDs have different purposes, which can affect which one you use to style HTML elements. CSS classes are meant to be reused…
  11. 11
    Specificity is the order by which the browser decides which CSS styles will be displayed. A best practice in CSS is to style elements while using the lowest degree of specificity, so that if an ele…
  12. 12
    When writing CSS rules, it’s possible to require an HTML element to have two or more CSS selectors at the same time. This is done by combining multiple selectors, which we will refer to as chaini…
  13. 13
    In addition to chaining selectors to select elements, CSS also supports selecting elements that are nested within other HTML elements. For instance, consider the following HTML: … ….
  14. 14
    In the last exercise, instead of selecting all h5 elements, you selected only the h5 elements nested inside the .description elements. This CSS selector was more specific than writing only h5. Addi…
  15. 15
    There is one thing that is even more specific than IDs: !important. !important can be applied to specific attributes instead of full rules. It will override any style no matter how specific it is…
  16. 16
    In order to make CSS more concise, it’s possible to add CSS styles to multiple CSS selectors all at once. This prevents writing repetitive code. For instance, the following code has repetitive st…
  17. 17
    Throughout this lesson, you learned how to select HTML elements with CSS and apply styles to them. Let’s review what you learned: - CSS can change the look of HTML elements. In order to do this, …
  1. 1
    In this lesson, you’ll learn the basic structure and syntax of CSS so that you can start styling web page elements.
  2. 2
    To style an HTML element using CSS, you need to write a CSS declaration inside the body of a CSS selector. h1 { color: blue; } The example above selects the element. Inside of the selector’s…
  3. 3
    If you’ve ever used a formatted word processor, chances are that you probably also used a feature that allowed you change the font you were typing in. Font refers to the technical term typeface , …
  4. 4
    Changing the typeface isn’t the only way to customize text. Often times, different sections of a web page are highlighted by modifying the font size. To change the size of text on your web page…
  5. 5
    In CSS, the font-weight property controls how bold or thin text appears. p { font-weight: bold; } In the example above, all paragraphs on the web page would appear bolded. The font-weight …
  6. 6
    No matter how much styling is applied to text (typeface, size, weight, etc.), text always appears on the left side of the browser. To align text we can use the text-align property. The text-align…
  7. 7
    Before discussing the specifics of color, it’s important to make two distinctions about color. Color can affect the following design aspects: - Foreground color - Background color Foreground co…
  8. 8
    Opacity is the measure of how transparent an element is. It’s measured from 0 to 1, with 1 representing 100%, or fully visible and opaque, and 0 representing 0%, or fully invisible. Opacity can b…
  9. 9
    CSS has the ability to change the background of an element. One option is to make the background of an element an image. This is done through the CSS property background-image. Its syntax looks lik…
  10. 10
    Incredible work! You used CSS to alter text and images throughout a website. Throughout this lesson, you learned concepts including: - CSS declarations are structured into property and value pair…

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