Css Stylesheet Class Explained in Detail

A CSS stylesheet class is a group of styles that can be applied to multiple HTML elements. It's a way to reuse styles across a website.

Think of a class like a label that you can attach to any number of elements, and then style them all at once. This makes maintenance and updates much easier.

Classes are defined in the CSS stylesheet, and then applied to elements in the HTML using the class attribute. For example, if you define a class called "header" in your CSS, you can apply that class to a header element in your HTML.

CSS selectors are the backbone of styling in .NET MAUI, allowing you to target specific elements with precision. A selector is a chain of one or more simple selectors separated by combinators.

There are several types of selectors supported by .NET MAUI, including type selectors, universal selectors, attribute selectors, ID selectors, and pseudo-classes. For example, the .class selector selects all elements with the StyleClass property containing 'header', while the #id selector selects all elements with StyleId set to email.

You can use combinators like white space, ">", and "+" to combine simple selectors and create more complex rules. For instance, StackLayout>ContentView>label.email selects all Label elements inside a StackLayout that is inside a ContentView.

Here are some examples of supported selectors:

Remember, selectors can be combined without limitation, so you can get very specific with your styling.

The selector reference is a crucial part of understanding CSS selectors. It's a list of supported selectors that you can use to target specific elements on your webpage.

The universal selector, denoted by an asterisk (*), matches any single element in the document tree. It's equivalent to using *.[lang=fr] or [lang=fr] in a selector.

You can use attribute selectors to match elements based on their attributes. For example, the selector *[lang=fr] matches all elements with a lang attribute set to fr.

Here's a list of supported selectors:

You can combine these selectors without limitation, such as StackLayout>ContentView>label.email.

Descendant selectors help match elements that are contained within other elements. They're made up of two or more selectors separated by white space.

For example, a descendant selector of the form "A B" matches when an element B is an arbitrary descendant of some ancestor element A. This means that A can be a parent, grandparent, or any other ancestor of B.

In the case of "H1 EM", the intention is to add emphasis to text by changing its color, but the effect will be lost if the EM is not directly contained within the H1. To fix this, we add a rule that sets the text color to blue whenever an EM occurs anywhere within an H1.

A descendant selector can match an element that is a grandchild or later descendant of another element. For instance, "DIV * P" matches a P element that is a grandchild or later descendant of a DIV element.

The white space in a descendant selector is not part of the universal selector; it's a combinator indicating that the ancestor element must be the parent of some other element, which must be an ancestor of the matched element.

A CSS stylesheet class is a powerful tool for styling your web pages, and understanding the different types of selectors is key to mastering it. There are several types of selectors, including element selectors, class selectors, and ID selectors.

Element selectors match specific HTML elements, such as H1 or label. They can be used to style individual elements or groups of elements.

Class selectors, denoted by a period (.) followed by a class name, match all elements with a specific class attribute. For example, .header would match all elements with a class attribute containing 'header'. Class selectors are case sensitive.

ID selectors, denoted by a number sign (#) followed by an ID name, match a single element with a specific ID attribute. For example, #email would match an element with an ID attribute set to 'email'. ID selectors are also case sensitive.

Here are the different types of selectors:

Universal selectors, denoted by an asterisk (*), match the name of any element type. They can be used to match any single element in the document tree, or in combination with other selectors to match more specific elements.

A style rule has two main parts: a selector and one or more declarations. The selector can be an element, class, or ID, and it's what determines which elements on the page are affected by the style.

An element-based style consists only of an HTML element, such as H1. This type of selector matches every instance of the element type in the document tree.

A class-based style is defined by a period (.) preceding the selector, like this: .class-name. This type of selector targets elements with the specified class.

An ID-based style is defined by a number sign (#) preceding the selector, like this: #id-name. This type of selector targets a single element with the specified ID.

Here are the different types of selectors in a concise table:

By understanding the different types of selectors, you can write more targeted and effective CSS rules that match the needs of your project.

A child selector matches when an element is the child of some element. It's made up of two or more selectors separated by ">".

The following rule sets the style of all P elements that are children of BODY. This is a simple example of a child selector in action.

A child selector can be combined with other selectors to create more complex rules. For example, it matches a P element that is a descendant of an LI; the LI element must be the child of an OL element; the OL element must be a descendant of a DIV.

In .NET MAUI, you can use a variety of CSS selectors to target specific elements in your application.

The universal selector (*) selects all elements, while a type selector (like label) selects all elements of a specific type, but not subclasses. You can also use an ID selector (#id) to select all elements with a specific ID, which is case sensitive.

You can combine multiple selectors to create more complex rules, like StackLayout>ContentView>label.email, which selects all Label elements inside a StackLayout and a ContentView.

The following selectors are unsupported: attribute selectors, @media and @supports, and : and :: pseudo-classes.

Here are some examples of supported selectors:

You can also use combinators to create more specific rules, like > (direct parent), + (directly after), and ~ (preceded by). These combinators are case insensitive.

Styles with matching selectors are applied consecutively, in definition order. Styles defined on a specific item are always applied last.

Pseudo-classes and pseudo-elements are two powerful concepts in CSS that allow you to style elements based on characteristics that lie outside the document tree.

In CSS 2.1, pseudo-elements create abstractions about the document tree beyond those specified by the document language. This allows style sheet designers to refer to information that would otherwise be inaccessible.

Pseudo-elements may also provide a way to assign style to content that does not exist in the source document, such as the :before and :after pseudo-elements.

Pseudo-classes, on the other hand, classify elements on characteristics other than their name, attributes, or content.

Some pseudo-classes are mutually exclusive, while others can be applied simultaneously to the same element.

Pseudo-class names are case-insensitive, making it easier to write style rules.

In CSS 2.1, pseudo-elements may only be appended after the last simple selector of the selector, while pseudo-classes are allowed anywhere in selectors.

Here are some common pseudo-classes used in CSS:

These pseudo-classes can be combined to create complex style rules, such as matching elements that are both in focus and hover states.

We can separate CSS styles from the HTML document and put them in their own file, which is known as an external CSS stylesheet. This is done by creating a new file with a .css extension and moving the CSS code from the HTML file to it.

A link element is then added to the HTML file to connect the two documents together. This allows the browser to load the CSS styles from the external file and apply them to the HTML document.

By keeping the CSS styles separate from the HTML, we can easily maintain and update the layout and design of our website.

Cascading Order is a fundamental concept in CSS that determines which style will be applied when multiple styles are specified for an HTML element.

In CSS, styles are read in a specific order of priority, with the highest priority being the inline style, which is defined directly within an HTML element.

The priority order is as follows:

This means that an inline style will override any other style declared in an external style sheet, internal style sheet, or even the browser's default value.

For example, if you define a style in an external style sheet to render text as blue, but then define an inline style to render the same text as red, the inline style will take precedence and the text will be displayed in red.

Using external CSS is a best practice for several reasons. It makes your code easier to read, manage, and debug by separating your HTML from your CSS.

With external CSS, you can make changes across your site by changing the CSS in one file. This is the most time-effective method.

External CSS is also the most SEO-friendly method. Storing CSS in another file makes your HTML file easier to read for search engines.

External CSS can help with load time by allowing a visitor's browser to cache the CSS file, making your website load faster on their next visit. It also makes HTML files smaller and quicker to load.

External CSS helps with accessibility because the HTML code is easier to parse by accessibility tools.

Grouping is a simple yet powerful technique that can make your CSS stylesheet more efficient and easier to maintain. In fact, it can condense multiple rules with identical declarations into one, making your code more concise.

This is particularly useful when you have multiple selectors that share the same styles. By grouping them, you can simplify your code and reduce repetition. For example, if you have three rules with identical declarations, you can group them into one.

The color of your CSS world is a crucial aspect of styling. You can use the color property to set the color of various elements, such as Button, DatePicker, and Entry, to a specific color like rgba(255, 0, 0, 0.3).

The background-color property is used to set the background color of an element, such as a Page, to a specific color like springgreen. The border-color property is used to set the border color of elements like Button, Frame, and ImageButton to a specific color like #9acd32.

Here's a list of valid values for the color, background-color, and border-color properties:

The initial value resets the color to its default value.

Color is a fundamental aspect of CSS, and understanding the various ways to represent colors is crucial for creating visually appealing and consistent designs.

X11 colors, which match CSS colors and .NET MAUI colors, are case insensitive.

You can also use hex colors, which come in different formats such as #rgb, #argb, #rrggbb, and #aarrggbb.

RGB colors are another option, represented as rgb(255,0,0) or rgb(100%,0%,0%), with values ranging from 0-255 or 0%-100%.

For more nuanced color control, you can use rgba colors, which include an opacity value, represented as rgba(255, 0, 0, 0.8) or rgba(100%, 0%, 0%, 0.8), with opacity values ranging from 0.0-1.0.

HSL and HSLA colors offer another approach, with HSL represented as hsl(120, 100%, 50%) and HSLA represented as hsl(120, 100%, 50%, .8), with HSL values ranging from 0-360 for hue and 0%-100% for saturation and lightness, and HSLA opacity values ranging from 0.0-1.0.

Here's a summary of the different color formats:

The CSS properties you can use in .NET MAUI are numerous, but some are more useful than others.

You can use the `align-content` property to control the alignment of items in a FlexLayout. This property has several valid values, including `stretch`, `center`, `spacebetween`, and `flex-end`.

The `background-color` property is used to set the background color of a VisualElement. You can set it to a color, like `springgreen`, or use the `initial` value to reset it to its default value.

To set the background image of a Page, you can use the `background-image` property and assign it a string value, like `bg.png`.

Some properties, like `border-color` and `border-radius`, have specific valid values. For example, `border-color` can be set to a color, like `#9acd32`, and `border-radius` can be set to a double value, like `10`.

Here's a list of some CSS properties and their valid values:

The `initial` value is a valid value for all properties, and it clears the value that was set from another style.