CS 511- Week 3: Topic 27-29

 CS 511-Web Engineering

Week 3

Topic 27-29

CS 511- Week 3: Topic 27-29

Topic 27:

A pseudo-element selector is a CSS selector that allows you to target and style a specific part of an element that doesn't exist explicitly in the HTML structure. It creates an imaginary element within the selected element and lets you apply styles to that imaginary element. Some common pseudo-element selectors include:

1. ::first-letter: This pseudo-element selects the first letter of a block-level element and allows you to apply styles specifically to that letter. It is often used for decorative purposes, such as creating drop-caps at the beginning of paragraphs.
2. ::first-line: This pseudo-element selects the first line of a block-level element and allows you to style that line independently. It is commonly used to apply special styles, such as different font properties or text decorations, to the first line of a paragraph.

A pseudo-class selector, on the other hand, is used to select and style elements based on their state or relationship to other elements. Some common pseudo-class selectors include:

1. :link: This pseudo-class selects links that have not been visited by the user. It is typically used to apply styles to links before they have been clicked.
2. :visited: This pseudo-class selects links that have been visited by the user. It allows you to style visited links differently from unvisited links, providing visual feedback to the user.
3. :focus: This pseudo-class selects elements that currently have input focus, such as text boxes or buttons. It is often used to apply specific styles to elements that are actively being interacted with by the user.
4. :hover: This pseudo-class selects elements that the mouse pointer is currently hovering over. It enables you to apply styles to elements when the user hovers over them, creating interactive and dynamic effects.
5. :active: This pseudo-class selects elements that are being activated or clicked by the user. It is typically used to provide immediate visual feedback when an element is being interacted with, such as changing the appearance of a button when it is clicked.
6. :checked: This pseudo-class selects form elements that are currently checked, such as radio buttons or checkboxes. It allows you to style checked elements differently, making it useful for customizing the appearance of form controls.
7. :first-child: This pseudo-class selects elements that are the first child of their parent element. It is commonly used to target and style the first element in a list or a group of elements, giving it a distinct appearance.

These pseudo-elements and pseudo-classes provide powerful options for targeting specific parts of elements or selecting elements based on their state or relationship. They enhance the capabilities of CSS and enable you to create more interactive and visually appealing web designs.

Topic 28:

CSS Selectors (Contextual):

A contextual selector, also known as a combinator, is a type of CSS selector that allows you to select elements based on their relationship to other elements in the HTML structure. There are three types of contextual selectors:

1. Descendant Selector: A descendant selector, denoted by a space between two selectors, allows you to select elements that are descendants of a specified ancestor element. When using the descendant selector, the styles defined will be applied to all elements that are inside the specified ancestor, regardless of their immediate parent-child relationship.
2. Child Selector (>): A child selector matches elements that are direct children of a specified parent element. It is represented by a greater-than sign (>), which separates the two selectors. For example, the selector "div > p" selects only the <p> elements that are immediate children of <div> elements. It does not select <p> elements that are nested further down the hierarchy.
3. Adjacent Sibling Selector (+): An adjacent sibling selector matches elements that are immediately following a specified element and share the same parent. It is represented by a plus sign (+) between two selectors. For example, the selector "h2 + p" selects the <p> element that directly follows an <h2> element. It applies styles to the first <p> element after each <h2>, but not to any other <p> elements.

These contextual selectors provide a way to target specific elements based on their relationship to other elements in the HTML structure. By using these selectors effectively, you can apply styles to elements in a more precise and targeted manner, enhancing the flexibility and control of your CSS styling.

Topic 29:

CSS Cascading:

CSS cascading refers to the process of determining how conflicting style rules are resolved and applied to elements on a web page. It involves three main principles: inheritance, specificity, and location.

1. Inheritance: Some CSS properties are inheritable, meaning that they affect not only the element they are applied to but also their descendant elements. For example, properties like font, color, list styles, and text properties are often inheritable. On the other hand, layout, sizing, border, background, and spacing properties are typically not inheritable. When an element inherits a property, it adopts the value of that property from its parent element. This allows for consistent styling throughout the document hierarchy.
2. Specificity: Specificity determines which style rule takes precedence when multiple rules could potentially apply to the same element. CSS uses a specificity value to compare selectors and determine which one is more specific. The more specific a selector is, the higher its specificity value and the higher its precedence. For example, an ID selector (#id) is more specific than a class selector (.class), and an inline style attribute has the highest specificity. When conflicting rules exist, the most specific rule will override others and apply its styles to the element.
3. Location: If inheritance and specificity cannot determine the precedence of conflicting rules, the principle of location comes into play. It states that the order in which the style rules are defined can affect their precedence. Inline styles defined directly on the element take the highest precedence, followed by embedded styles within the <style> tags in the HTML document. External style sheets defined in <link> elements are applied next. When conflicting rules have the same specificity, the latest rule defined will override earlier rules.

To illustrate these principles, consider an example where conflicting font and color properties are defined for a <body> element and its child elements. If the <body> element has an Arial font and red text color, but a <div> element within it has a different font and color defined, the properties defined for the <div> element will take precedence due to their specificity. Similarly, if an inline style is added to override a rule defined in an external style sheet, the inline style will take precedence due to its location within the HTML structure.

Understanding the cascading nature of CSS helps developers manage and control styles effectively, ensuring consistent and desired visual results across web pages.

Assessment:

CS 511- Week 3: Topic 27-29

1. Which CSS selector is used to select the first letter of a block-level element? 

A):first-child 

B)::first-letter 

C):first-line 

Answer: B)::first-letter

2. Which pseudo-class selector is used to select links that have not been visited? 

A):visited 

B):hover 

C):link 

Answer: C):link

3. When conflicting style rules have the same specificity, which principle determines their precedence?

A) Inheritance 

B) Specificity 

C) Location 

Answer: C) Location

4. Which CSS property is typically inheritable? 

A) background-color 

B) width 

C) color 

Answer: C) color

THE END 😊