Notes

Getting CSS Into Your HTML

<!-- example.html -->
<!DOCTYPE html>
<html>
  <head>
    <link
      rel="stylesheet"
      href="https://cdnjs.cloudflare.com/ajax/libs/normalize/3.0.3/normalize.min.css"
    />
    <link rel="stylesheet" href="/styles/site.css" />
  </head>
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->


<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->
<!--------------------------------------------------------------------------------------------------->


  <body></body>
</html>

To connect your CSS sheet to your HTML page, use the link tag like so.
Many developers use External pre-written CSS stylesheets for consistent design.
You can connect multiple stylesheets.

CSS Selectors

CSS Selector : Applies styles to a specific DOM element(s), there are various types:
- Type Selectors : Matches by node name.
- Class Selectors : Matches by class name.
- ID Selectors : Matches by ID name.
- Universal Selectors : Selects all HTML elements on a page.
- Attribute Selectors : Matches elements based on the prescence or value of a given attribute. (i.e. a[title] will match all a elements with a title attribute)

/* Type selector */
div {
  background-color: #000000;
}

/* Class selector */
.active {
  color: #ffffff;
}

/* ID selector */
#list-1 {
  border: 1px solid gray;
}

/* Universal selector */
* {
  padding: 10px;
}

/* Attribute selector */
a[title] {
  font-size: 2em;
}

Class Selectors

Used to select all elements of a certain class denoted with a .[class name]
You can assign multiple classes to a DOM element by separating them with a space.

Compound Class Selectors

To get around accidentally selecting elements with multiple classes beyond what we want to grab we can chain dots.
TO use a compound class selector just append the classes together when referencing them in the CSS.

<div class="box yellow"></div>
<div class="box orange"></div>
<div class="circle orange"></div>

i.e. .box.yellow will select only the first element.
KEEP IN MIND that if you do include a space it will make the selector into a descendant selector.

h1#heading,
h2.subheading {
  font-style: italic;
}

When we want to target all h1 tags with the id of heading.

CSS Combinators

CSS Combinators are used to combine other selectors into more complex or targeted selectors - they are very powerful!

Be careful not to use too many of them as they will make your CSS far too complex.

Descendant Selectors
- Seperated by a space.
- Selects all descendants of a parent container.

Direct Child Selectors

Indicated with a >.
Different from descendants because it only affects the direct children of an element.

.menu > .is-active {
  background-color: #ffe0b2;
}

<body>
  <div class="menu">
    <div class="is-active">Belka</div>
    <div>
      <div class="is-active">Strelka</div>
    </div>
  </div>
</body>
<div class="is-active">
  Laika
</div>
</body>

Belka would be the only element selected.

Adjacent Sibling Selectors

Uses the + symbol.
Used for elements that directly follow one another and who both have the same parent.

  h1 + h2 {
font-style: italic;
  }

<h1>Big header</h1>
<h2>This one is styled because it is directly adjacent to the H1</h2>
<h2>This one is NOT styled because there is no H1 right before it</h2>

Pseudo-Classes

Pseudo-Class : Specifies a special state of the seleted element(s) and does not refer to any elements or attributes contained in the DOM.
- Format is a Selector:Pseudo-Class Name or A:B
```
a:hover {
  font-family: "Roboto Condensed", sans-serif;
  color: #4fc3f7;
  text-decoration: none;
  border-bottom: 2px solid #4fc3f7;
}
```
- Some common pseudo-classes that are frequently used are:
  - active : ‘push down’, when ele are activated.
  - checked : applies to things like radio buttons or checkbox inputs.
  - disabled : any disabled element.
  - first-child : first element in a group of children/siblings.
  - focus : elements that have current focus.
  - hover : elements that have cursor hovering over it.
  - invalid : any form elements in an invalid state from client-side form validation.
  - last-child : last element in a group of children/siblings.
  - not(selector) : elements that do not match the provided selector.
  - required : form elements that are required.
  - valid : form elements in a valid state.
  - visited : anchor tags of whih the user has already been to the URL that the href points to.

Pseudo-Selectors

Used to create pseudo-elements as children of the elements to which the property applies.
- ::after
- ::before

<style>
  p::before {
    background-color: lightblue;
    border-right: 4px solid violet;
    content: ":-) ";
    margin-right: 4px;
    padding-left: 4px;
  }
</style>
<p>This is the first paragraph</p>
<p>This is the second paragraph</p>
<p>This is the third paragraph</p>

Will add some blue smiley faces before the p tag elements.

CSS Rules

CSS Rule : Collection of single or compound selectors, a curly brace, zero or more properties
CSS Rule Specificity : Sometimes CSS rules will contain multiple elements and may have overlapping properties rules for those same elements - there is an algorithm in CSS that calculates which rule takes precendence.
- The Four Number Calculation : listed in increasing order of importance.
- 1. Who has the most IDs? If no one, continue.
- 1. Who has the most classes? If no one, continue.
- 1. Who has the most tags? If no one, continue.
- 1. Last Read in the browser wins.

<style>
  .box {
    width: 50px;
    height: 50px;
    border: 1px solid black;
  }
  .orange {
    background-color: orange;
  }
  .yellow {
    background-color: yellow;
    border: 1px solid purple;
  }
</style>
<div class="box yellow"></div>
<div class="box orange"></div>

Coming back to our example where all the CSS Rules have tied, the last step 4 wins out so our element will have a purple border.

CSS: Type, Properties, and Imports

Typography

font-family : change the font.
- Remember that not all computers have the same fonts on them.
- You can import web fonts via an api by using
  - @import url('https://fonts.googleapis.com/css2?family=Liu+Jian+Mao+Cao&display=swap'); and pasting it st the top of your CSS file.
  - And then reference it in your font-family.
font-size : Changes the size of your font.
- Keep in mind the two kind of units CSS uses:
  - Absolute : Pixels, Points, Inches, Centimeters.
  - Relative : Em, Rem.
    - Em: Calulating the size relative to the previous div (bubbles down)
    - Rem: Calulates relative to the parent element always.
font-style : Used to set a font to italics.
font-weight : Used to make a font bold.
text-align : Used to align your text to the left, center, or right.
text-decoration : Use to put lines above, through, or under text. Lines can be solid, dashed, or wavy!
text-transform : Used to set text to all lowercase, uppercase, or capitalize all words.

Background-Images

You can use the background-image property to set a background image for an element.

CSS: Colors, Borders, and Shadows

Colors

You can set colors in CSS in three popular ways: by name, by hexadecimal RGB value, and by their decimal RGB value.
rgba() is used to make an rbg value more transparent, the a is used to specify the alpha channel.
Color : Property used to change the color of text.
Background-Color : Property to change the backgrounf color of an element.

Borders

Borders take three values: The width of the border, the style (i.e. solid, dotted, dashed), color of the border.

Shadows

There are two kinds of shadows in CSS: box shadows and text shadows.
- Box refers to HTML elements.
- Text refers to text.
- Shadows take values such as, the horizontal & vertical offsets of the shadow, the blur radius of the shadow, the spread radius, and of course the colors.