CSS - References

Ethan D. - May 31, 2024

Types of CSS References

Element References

In CSS, you can reference HTML elements directly to apply styles to them. This is known as element referencing. To reference an element, you use the element's name followed by the desired styles within curly braces. The syntax for element references is:

Example: Element Reference Syntax

element {
  property: value;
}

To apply styles to all <p> elements on a page, you would use this CSS code:

Example: Applying Styles to `<p>` Elements

p {
  color: blue;
  font-size: 16px;
}

This would make all paragraphs on the page have blue text color and a font size of 16 pixels.

Class References

CSS classes allow you to group HTML elements and apply styles to them collectively. To reference a class in CSS, you use the dot (.) followed by the class name. The syntax for class references is:

Example: Class Reference Syntax

.class-name {
  property: value;
}

If you have HTML elements with a class of "highlight", you can apply styles to those elements using this CSS code:

Example: Applying Styles to .highlight Class

.highlight {
  background-color: yellow;
  font-weight: bold;
}

This would give all elements with the "highlight" class a yellow background color and bold font weight.

ID References

CSS IDs are used to uniquely identify HTML elements and apply specific styles to them. To reference an ID in CSS, you use the hash (#) followed by the ID name. The syntax for ID references is:

Example: ID Reference Syntax

#id-name {
  property: value;
}

If you have an HTML element with an ID of "header", you can apply styles to that element using this CSS code:

Example: Applying Styles to #header ID

#header {
  background-color: #333;
  color: white;
  padding: 20px;
}

This would give the element with the ID "header" a dark gray background color, white text color, and a padding of 20 pixels on all sides.

It's important to note that IDs should be unique within a page, meaning you should not have multiple elements with the same ID. IDs are meant for targeting specific individual elements, while classes are used for grouping and applying styles to multiple elements.

Specificity and Cascading Order

CSS specificity is a set of rules that determines which styles are applied to an element when there are conflicting styles. It is important to understand specificity to control how styles are applied and to avoid unexpected results.

The cascading order of CSS references determines the order in which styles are applied to an element. The cascading order follows these rules, from highest priority to lowest:

Inline styles (styles applied directly to the element using the style attribute)
ID selectors
Class selectors
Element selectors

When there are conflicting styles, the style with the highest specificity will be applied. Inline styles have the highest specificity, followed by ID selectors, class selectors, and element selectors.

Specificity and Cascading Order Example

<style>
  p {
    color: blue;
  }

  .highlight {
    color: red;
  }

  #special {
    color: green;
  }
</style>

<p>This is a regular paragraph.</p>
<p class="highlight">This paragraph has the "highlight" class.</p>
<p id="special" class="highlight">This paragraph has the "special" ID and the "highlight" class.</p>

Paragraph	Applied Style	Explanation
First paragraph	Blue text	Styled using an element selector (`p`).
Second paragraph	Red text	The class selector (`.highlight`) has higher specificity than the element selector.
Third paragraph	Green text	The ID selector (`#special`) has the highest specificity, overriding both the class selector and the element selector.

When there are equal-specificity selectors, the cascading order comes into play. The style that appears later in the stylesheet or the one that is more specific will take precedence.

It's important to consider specificity and cascading order when writing CSS to make sure that styles are applied correctly and to avoid unintended overrides. You can use the specificity calculator to determine the specificity score of a selector and make informed decisions about which styles will take precedence.

Combining CSS References

In CSS, you can combine element, class, and ID references to create more specific and targeted styles. By combining these references, you can apply styles to elements that match multiple criteria. This approach is useful when you want to style elements based on both their type and their assigned classes or IDs.

To combine CSS references, you write them together without any spaces between them. The syntax for combining references is:

Example: Syntax for combining CSS references

element.class {
  property: value;
}

element#id {
  property: value;
}

.class#id {
  property: value;
}

Example: Combining element and class

p.highlight {
  background-color: yellow;
  font-weight: bold;
}

In this example, the styles will only be applied to <p> elements that have the class "highlight". Other elements with the "highlight" class will not be affected.

Example: Combining element and ID

div#header {
  background-color: #333;
  color: white;
  padding: 20px;
}

This example combines an element reference (div) with an ID reference (#header). The styles will only be applied to the <div> element with the ID "header".

Example: Combining class and ID

.menu#main-menu {
  list-style-type: none;
  margin: 0;
  padding: 0;
}

In this example, the styles will only be applied to an element that has both the class "menu" and the ID "main-menu". This is a very specific combination and is less common than combining element and class or element and ID references.

Combining CSS references allows you to create more specific styles and target elements based on multiple attributes. However, it's important to use this technique sparingly and only when necessary to avoid creating overly complex and difficult-to-maintain stylesheets. It's also important to consider the specificity of the combined references and how they will interact with other styles applied to the same elements.

CSS Reference Selectors

Attribute Selectors

CSS attribute selectors let you select elements based on their attributes or attribute values. This is useful when you want to style elements that have specific attributes or attribute values. The syntax for attribute selectors is:

Example: Basic attribute selectors

[attribute] {
  property: value;
}

[attribute="value"] {
  property: value;
}

To style all <a> elements that have a target attribute:

Example: Styling based on an attribute

a[target] {
  color: red;
}

To style <img> elements with a specific alt attribute value:

Example: Styling based on specific attribute values

img[alt="logo"] {
  border: 1px solid black;
}

Pseudo-class Selectors

Pseudo-class selectors let you select elements based on their state or position. They style elements when they are in a specific state or position. The syntax for pseudo-class selectors is:

Example: Basic pseudo-class selectors

element:pseudo-class {
  property: value;
}

One common pseudo-class selector is the :hover selector, which styles an element when the mouse hovers over it:

Hover pseudo-class example

a:hover {
  text-decoration: underline;
}

Other examples of pseudo-class selectors:

:active - styles an element when it is being activated (e.g., clicked)
:focus - styles an element when it has focus (e.g., a form input)
:first-child - styles the first child element of its parent
:nth-child(n) - styles the nth child element of its parent

Pseudo-element Selectors

Pseudo-element selectors let you select and style specific parts of an element. They add content or style specific parts of an element. The syntax for pseudo-element selectors is:

Example: Basic pseudo-element selectors

element::pseudo-element {
  property: value;
}

One common pseudo-element selector is the ::before selector, which inserts content before an element:

Before pseudo-element example

p::before {
  content: "Read this: ";
  font-weight: bold;
}

Another example is the ::first-letter selector, which styles the first letter of an element:

First letter pseudo-element example

p::first-letter {
  font-size: 24px;
  font-weight: bold;
}

Other examples of pseudo-element selectors:

::after - inserts content after an element
::first-line - styles the first line of an element
::selection - styles the selected text of an element

Attribute selectors, pseudo-class selectors, and pseudo-element selectors provide ways to select and style elements based on their attributes, states, positions, and specific parts. They let you create more targeted and dynamic styles in your CSS.

CSS Reference Specificity Calculator

CSS specificity determines which styles are applied to an element when there are conflicting styles. Understanding specificity is important for writing CSS and avoiding unexpected results. The CSS specificity calculator helps you calculate the specificity score of a selector and determine which styles will take precedence.

To calculate the specificity score, consider the following factors:

Inline styles (styles applied directly to the element using the style attribute)
ID selectors
Class selectors, attribute selectors, and pseudo-class selectors
Element selectors and pseudo-element selectors

Each factor is assigned a value and the specificity score is calculated by combining these values:

Factor	Value
Inline styles	1000 points
ID selectors	100 points
Class selectors, attribute selectors, and pseudo-class selectors	10 points
Element selectors and pseudo-element selectors	1 point

To calculate the specificity score of a selector, count the number of each type of selector and multiply it by its corresponding value. Then, add up the results to get the total specificity score.

Example: Calculating Specificity Score

/* Selector: p.highlight #special */
- Inline styles: 0
- ID selectors: 1 (100 points)
- Class selectors: 1 (10 points)
- Element selectors: 1 (1 point)

Specificity score: (0 * 1000) + (1 * 100) + (1 * 10) + (1 * 1) = 111

In this example, the selector p.highlight #special has a specificity score of 111. It has one ID selector (#special), one class selector (.highlight), and one element selector (p).

Here are a few more examples of calculating specificity scores:

Example 1: .menu li

/* Selector: .menu li */
- Inline styles: 0
- ID selectors: 0
- Class selectors: 1 (10 points)
- Element selectors: 1 (1 point)

Specificity score: (0 * 1000) + (0 * 100) + (1 * 10) + (1 * 1) = 11

Example 2: #header a:hover

/* Selector: #header a:hover */
- Inline styles: 0
- ID selectors: 1 (100 points)
- Class selectors: 1 (10 points for the pseudo-class selector)
- Element selectors: 1 (1 point)

Specificity score: (0 * 1000) + (1 * 100) + (1 * 10) + (1 * 1) = 111

When there are conflicting styles, the selector with the highest specificity score will take precedence. If two selectors have the same specificity score, the one that appears later in the stylesheet will be applied.

Using the CSS specificity calculator helps you understand how specificity works and makes it easier to write CSS that behaves as expected. By calculating specificity scores, you can make decisions about which styles will be applied to your elements and avoid unintended overrides.