Technical Paper on HTML/CSS
Tags: webdev, javascript
Published: 2023-05-24 12:48:25


## CSS Box Model:

The CSS box model is a way of representing HTML elements in CSS. It consists of four parts:

* **Content** - This is the actual content of the element, such as text or images.
* **Padding** - This is the space between the content and the border.
* **Border** - This is the line that surrounds the content and padding.
* **Margin** - This is the space between the border and other elements on the page.

The following image shows the different parts of the box model:

![CSS box model](http://t0.gstatic.com/images?q=tbn:ANd9GcR8rHP8rchKSRNlU0ogs0VIIOqJZ3-6Q_yVszyoLLPj53vJh3oP&s)

The size of the box is determined by the sum of the widths and heights of the content, padding, border, and margin. For example, if the content is 100px wide, the padding is 20px, the border is 10px, and the margin is 10px, then the total width of the box will be 140px.

The CSS box model can be used to control the appearance of HTML elements in a variety of ways. For example, you can use the `padding` property to add space around the content, the `border` property to add a border around the element, and the `margin` property to add space between the element and other elements on the page.

Here are some examples of how to use the CSS box model to style HTML elements:







CSS

```
p {
  padding: 10px;
  border: 1px solid black;
  margin: 5px;
}

```



This code will add a 10px padding, a 1px solid black border, and a 5px margin to all paragraphs on the page.

CSS

```
div {
  padding: 10px;
  border: 1px solid black;
  margin: 5px;
  background-color: blue;
}

```

This code will add a 10px padding, a 1px solid black border, a 5px margin, and a blue background color to all div elements on the page.




The CSS box model is a powerful tool that can be used to control the appearance of HTML elements in a variety of ways. By understanding the different parts of the box model and how to use the CSS properties that control them, you can create custom styles that will make your web pages look their best.

#  -   Inline versus Block Elements. Examples:
some examples of inline and block elements in CSS:

**Inline Elements**

-   `<a>`
-   `<img>`
-   `<span>`
-   `<br>`
-   `<em>`
-   `<strong>`

**Block Elements**

-   `<div>`
-   `<p>`
-   `<h1>`
-   `<h2>`
-   `<ul>`
-   `<li>`

Inline elements are displayed inline with the surrounding text, while block elements start on a new line and take up the full width of their container.

Here is an example of how inline and block elements are displayed:

HTML

```
<p>This is a paragraph.</p>

<div>This is a div element.</div>

<a href="#">This is a link.</a>

```


The paragraph will be displayed on a new line, while the div element and the link will be displayed inline with the surrounding text.

You can use the `display` property to change the display type of an element. For example, the following code will change the display type of the div element to inline:

CSS

```
div {
  display: inline;
}

```



This will cause the div element to be displayed inline with the surrounding text, just like the link element.

You can also use the `display` property to create custom layouts. For example, the following code will create a two-column layout:

CSS

```
div {
  display: inline-block;
}

```

This will cause the div elements to be displayed side-by-side, with a small gap between them.

The `display` property is a powerful tool that can be used to control the layout of your web pages. By understanding the different display types and how to use them, you can create custom layouts that will make your pages look their best.


#   Positioning: Relative/Absolute:

-   **Static:**  The default value. Elements with static positioning are placed in the document flow according to their source order.
-   **Relative:**  Elements with relative positioning are positioned relative to their original position in the document flow. This means that they can be moved around using the  `top`,  `left`,  `bottom`, and  `right`  properties.
-   **Absolute:**  Elements with absolute positioning are positioned relative to the nearest positioned ancestor element. If there is no positioned ancestor element, then the element is positioned relative to the  `html`  element. Absolute positioned elements are removed from the document flow, and they do not affect the layout of other elements on the page.
-   **Fixed:**  Elements with fixed positioning are positioned relative to the viewport. This means that they stay in the same place on the page, even when the user scrolls. Fixed positioned elements are also removed from the document flow.

Here is an example of how to use relative positioning to move an element 10 pixels to the right:

Code snippet

```
.my-element {
  position: relative;
  right: 10px;
}

```

Here is an example of how to use absolute positioning to position an element 10 pixels to the right of its nearest positioned ancestor:

Code snippet

```
.my-element {
  position: absolute;
  right: 10px;
}
```


#    Common CSS structural classes:

-   **:first-child**  - Selects the first child of its parent.
-   **:last-child**  - Selects the last child of its parent.
-   **:only-child**  - Selects an element that is the only child of its parent.
-   **:nth-child(n)**  - Selects every nth child of its parent. For example,  `:nth-child(2)`  will select every second child.
-   **:nth-of-type(n)**  - Selects every nth element of a particular type within its parent. For example,  `:nth-of-type(2) div`  will select every second div within its parent.
-   **:nth-last-child(n)**  - Selects every nth child of its parent, counting from the last child. For example,  `:nth-last-child(2)`  will select every second child, starting from the last child.
-   **:nth-last-of-type(n)**  - Selects every nth element of a particular type within its parent, counting from the last child. For example,  `:nth-last-of-type(2) div`  will select every second div, starting from the last div.
-   **:first-of-type**  - Selects the first element of a particular type within its parent. For example,  `:first-of-type div`  will select the first div within its parent.
-   **:last-of-type**  - Selects the last element of a particular type within its parent. For example,  `:last-of-type div`  will select the last div within its parent.
-   **:only-of-type**  - Selects an element that is the only element of a particular type within its parent. For example,  `:only-of-type div`  will select a div if it is the only div within its parent.


#   Common CSS styling classes:
-   **.active:**  This class is used to style the currently active element, such as a link or button.
-   **.error:**  This class is used to style elements that have errors, such as form fields with invalid input.
-   **.info:**  This class is used to style elements that contain informational content.
-   **.success:**  This class is used to style elements that have been successfully processed, such as form submissions.
-   **.warning:**  This class is used to style elements that contain warnings or cautions.

These are just a few examples of common CSS styling classes. There are many other possible classes that can be used to style different elements on a web page.

Here are some examples of how these classes can be used:

CSS

```
.active {
  color: red;
  font-weight: bold;
}

.error {
  background-color: red;
  color: white;
}

.info {
  background-color: lightblue;
  color: black;
}

.success {
  background-color: green;
  color: white;
}

.warning {
  background-color: yellow;
  color: black;
}

```


These styles can be applied to any element on a web page by adding the appropriate class to the element's HTML tag. For example, to style a link as active, you would add the `active` class to the `a` tag.

HTML

```
<a href="#">This is an active link</a>

```



The CSS styles would then be applied to this link, making it appear red and bold.

By using CSS styling classes, you can easily style different elements on a web page. This makes it possible to create a consistent look and feel for your website.

#    CSS Specificity:
CSS specificity is a way of determining which CSS rule will be applied to an element when there are multiple rules that could apply. The rule with the highest specificity will be applied.

Specificity is calculated by counting the number of IDs, classes, and elements in the selector. The more of each type of selector, the higher the specificity.

For example, the following selector has a specificity of `1000`:

Code snippet

```
#myID.myClass

```

This is because it has one ID selector (`#myID`) and one class selector (`.myClass`).

The following selector has a specificity of `10`:

Code snippet

```
.myClass

```



This is because it has one class selector (`.myClass`).

The following selector has a specificity of `1`:

Code snippet

```
div

```


This is because it has one element selector (`div`).

If there are two rules that could apply to an element, the rule with the higher specificity will be applied. For example, the following two rules could both apply to an element:

Code snippet

```
#myID.myClass {
  color: red;
}

.myClass {
  color: blue;
}

```


The first rule has a specificity of `1000` and the second rule has a specificity of `10`. Therefore, the first rule will be applied and the element will be red.

You can use specificity to override other CSS rules. For example, if you want to make sure that an element always has a certain color, you can use a rule with a high specificity. For example, the following rule will always make the element red, no matter what other rules are applied:

Code snippet

```
#myID {
  color: red;
}

```


You can also use specificity to make sure that a rule only applies to a certain element or set of elements. For example, the following rule will only apply to the element with the ID `myID`:

Code snippet

```
#myID {
  color: red;
}

```


Specificity can be a bit confusing at first, but it is a very powerful tool that can help you control how CSS rules are applied.


#   CSS Responsive Queries:
  
CSS responsive queries are a way to control how CSS styles are applied to a web page based on the size of the screen. This allows you to create a website that looks good on all devices, from large desktop monitors to small mobile phones.

To use CSS responsive queries, you need to use the `@media` rule. The `@media` rule allows you to specify a set of CSS rules that will only be applied if the screen meets certain criteria. For example, you could use the `@media` rule to specify a different layout for a mobile phone than you would for a desktop computer.

The syntax for the `@media` rule is as follows:

Code snippet

```
@media media_query {
  /* CSS rules */
}

```



The `media_query` is a string that specifies the criteria that the screen must meet in order for the CSS rules to be applied. For example, the following `media_query` would specify that the CSS rules should only be applied if the screen is less than 600 pixels wide:

Code snippet

```
@media screen and (max-width: 600px) {
  /* CSS rules */
}

```

You can use a variety of media queries to specify different criteria. For example, you could use the `min-width` media query to specify that the CSS rules should only be applied if the screen is at least a certain width. You could also use the `orientation` media query to specify that the CSS rules should only be applied if the screen is in landscape or portrait mode.

Once you have defined your `@media` rule, you can then specify the CSS rules that you want to apply. These rules will only be applied if the screen meets the criteria that you specified in the `media_query`.

For example, the following code would specify that the `h1` element should be displayed in a larger font size on mobile phones:

Code snippet

```
@media screen and (max-width: 600px) {
  h1 {
    font-size: 2em;
  }
}

```


CSS responsive queries are a powerful tool that can help you create a website that looks good on all devices. By using CSS responsive queries, you can ensure that your website is accessible to everyone, regardless of the device they are using.

# Flexbox/Grid:

Flexbox and Grid are two different CSS layout models that can be used to create complex and responsive layouts.

Flexbox is a newer layout model that is designed for flexibility and responsiveness. It is based on the concept of a flex container, which can contain any number of flex items. The flex items can be arranged in a single row or column, or they can be arranged in a grid.

Grid is an older layout model that is designed for more complex layouts. It is based on the concept of a grid container, which can contain any number of grid items. The grid items can be arranged in a grid of any size, and they can be positioned anywhere in the grid.

Both Flexbox and Grid are powerful layout models that can be used to create complex and responsive layouts. However, they have different strengths and weaknesses.

Flexbox is a good choice for layouts that need to be flexible and responsive. It is easy to learn and use, and it can be used to create a wide variety of layouts.

Grid is a good choice for layouts that need to be more complex. It is more powerful than Flexbox, and it can be used to create layouts that are not possible with Flexbox.

Ultimately, the best choice for you will depend on the specific needs of your layout. If you need a flexible and responsive layout, then Flexbox is a good choice. If you need a more complex layout, then Grid is a good choice.

Here are some examples of how Flexbox and Grid can be used to create layouts:

**Flexbox**

-   A simple layout with a header, body, and footer:

Code snippet

```
<div class="container">
  <header>
    <h1>This is the header</h1>
  </header>
  <main>
    <p>This is the main content</p>
  </main>
  <footer>
    <p>This is the footer</p>
  </footer>
</div>

```

-   A layout with a sidebar and main content area:

Code snippet

```
<div class="container">
  <aside class="sidebar">
    <ul>
      <li><a href="#">This is a link</a></li>
      <li><a href="#">This is another link</a></li>
      <li><a href="#">This is one more link</a></li>
    </ul>
  </aside>
  <main>
    <p>This is the main content</p>
  </main>
</div>

```



**Grid**

-   A simple layout with a grid of images:

Code snippet

```
<div class="container">
  <div class="row">
    <div class="col-md-4">
      <img src="image1.jpg" alt="Image 1">
    </div>
    <div class="col-md-4">
      <img src="image2.jpg" alt="Image 2">
    </div>
    <div class="col-md-4">
      <img src="image3.jpg" alt="Image 3">
    </div>
  </div>
</div>

```

-   A layout with a grid of images and text:

Code snippet

```
<div class="container">
  <div class="row">
    <div class="col-md-4">
      <img src="image1.jpg" alt="Image 1">
      <h2>This is the title</h2>
      <p>This is the text</p>
    </div>
    <div class="col-md-4">
      <img src="image2.jpg" alt="Image 2">
      <h2>This is another title</h2>
      <p>This is another text</p>
    </div>
    <div class="col-md-4">
      <img src="image3.jpg" alt="Image 3">
      <h2>This is one more title</h2>
      <p>This is one more text</p>
    </div>
  </div>
</div>

```

As you can see, both Flexbox and Grid can be used to create a wide variety of layouts. The best choice for you will depend on the specific needs of your layout.



#    Common header meta tags:

-   **Title:**  The title meta tag is used to specify the title of the page. This title is displayed in the browser's title bar and in search engine results pages (SERPs).

HTML

```
<meta name="title" content="This is the title of the page">

```



-   **Description:**  The description meta tag is used to provide a brief description of the page. This description is displayed in SERPs, and it can help users decide whether or not to click on your link.

HTML

```
<meta name="description" content="This is a brief description of the page">

```



-   **Keywords:**  The keywords meta tag is used to specify the keywords that are relevant to the page. This information can be used by search engines to index your page and to rank it in search results.

HTML

```
<meta name="keywords" content="keyword1, keyword2, keyword3">

```


-   **Robots:**  The robots meta tag is used to control how search engines crawl and index your page. For example, you can use the robots meta tag to prevent search engines from crawling your sitemap or from indexing your contact page.

HTML

```
<meta name="robots" content="index, follow">

```


-   **Viewport:**  The viewport meta tag is used to control the initial size of the browser window. This can be useful for mobile devices, where you may want to specify a smaller initial window size.

HTML

```
<meta name="viewport" content="width=device-width, initial-scale=1">

```


-   **Content-Type:**  The Content-Type meta tag is used to specify the MIME type of the page. This information is used by the browser to determine how to render the page.

HTML

```
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

```

-   **Refresh:**  The Refresh meta tag is used to automatically refresh the page after a specified amount of time. This can be useful for pages that display news or other time-sensitive information.

HTML

```
<meta http-equiv="refresh" content="30">

```


-   **Author:**  The Author meta tag is used to specify the author of the page. This information can be displayed in SERPs, and it can help users to identify the source of the information.

HTML

```
<meta name="author" content="John Doe">

```

-   **Copyright:**  The Copyright meta tag is used to specify the copyright information for the page. This information can be displayed in SERPs, and it can help users to understand the terms of use for the page.

HTML

```
<meta name="copyright" content="Copyright 2023, John Doe">

```



-   **Noindex:**  The Noindex meta tag is used to prevent search engines from indexing the page. This can be useful for pages that are not intended to be indexed, such as login pages or private pages.

HTML

```
<meta name="robots" content="noindex">

```


-   **Nofollow:**  The Nofollow meta tag is used to prevent search engines from following links on the page. This can be useful for pages that contain spammy or irrelevant links.

HTML

```
<a href="https://www.spammywebsite.com" rel="nofollow">This is a spammy link</a>

```


These are just a few of the most common header meta tags. There are many other meta tags that can be used, and the specific meta tags that you use will depend on the needs of website.

# Inheritence:
Inheritance in CSS and HTML is the ability of an element to inherit properties from its parent element. This can be used to save time and effort when styling a web page, as you only need to specify the properties once on the parent element and they will be inherited by all child elements.

To inherit a property in CSS, you use the `inherit` keyword. For example, the following code will set the font size of all `p` elements to 16px:

CSS

```
p {
  font-size: 16px;
}

```


This will also set the font size of all child elements of `p` elements, such as `span` elements.

In HTML, inheritance is used to determine the default values of attributes. For example, the `href` attribute of the `a` element has a default value of `#`. This means that if you do not specify an `href` attribute on an `a` element, it will link to the current page.

Inheritance can be a powerful tool when used correctly. However, it is important to understand how it works so that you can avoid unintended consequences. For example, if you set the `color` property of a parent element to `red`, all child elements will also be red, even if you have explicitly set the `color` property of a child element to a different color.

To avoid this, you can use the `!important` keyword to override the inherited value of a property. For example, the following code will set the `color` property of the `span` element to `blue`, even though the `color` property of the `p` element is set to `red`:

CSS

```
p {
  color: red;
}

span {
  color: blue !important;
}
```