1.0.1 • Published 1 year ago

learn-css v1.0.1

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Last release
1 year ago

Learn CSS

CSS - Stands for Cascading Style Sheets

CSS describes how HTML elements are to be displayed on screen, paper, or in other media CSS saves a lot of work. It can control the layout of multiple web pages all at once External stylesheets are stored in CSS files.

CSS Syntax

h1 {
    color: #000000;
}
/* Where h1 is selector, color is property, and #000000 is value. Both with property and value are declaration. */

Seectors

Used to "find" (or select) the HTML elements you want to style.

CSS Selectors are divided into five categories :

Simple selectors - select elements based on name, id, class

Combinator selectors - select elements based on a specific relationship between them

Pseudo-class selectors - select elements based on a certain state

Pseudo-elements selectors - select and style a part of an element

Attribute selectors - select elements based on an attribute or attribute value

Here are most basic CSS selectors used :

1. CSS element Selector - selects HTML elements based on the element name.

p {
  text-align: center;
  color: blue;
}

2. CSS id Selector - uses the id attribute of an HTML element to select a specific element.

To select an element with a specific id, write a hash (#) character, followed by the id of the element.

#para1 {
  text-align: center;
  color: blue;
}

3. CSS class Selector - selects HTML elements with a specific class attribute.

To select elements with a specific class, write a period (.) character, followed by the class name.

.center {
  text-align: center;
  color: blue;
}

You can also specify that only specific HTML elements should be affected by a class.

p.center {
  text-align: center;
  color: blue;
}

HTML elements can also refer to more than one class.

<p class="center large">This paragraph refers to two classes.</p>

4. CSS Universal Selector - selects all HTML elements on the page.

* {
  text-align: center;
  color: blue;
}

5. CSS Grouping Selector - selects all the HTML elements with the same style definitions.

h1, h2, p {
  text-align: center;
  color: blue;
}

Three Ways to Add CSS

1. External CSS - With an external style sheet, you can change the look of an entire website by changing just one file!

<!--FileName: index.html-->
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="style.css">
</head>
<body>

<h1>This is a heading</h1>
<p>This is a paragraph.</p>

</body>
</html>
/* Filename: styles.css*/
body {
  background-color: lightblue;
}

h1 {
  color: blue;
  margin-left: 20px;
}

2. Internal CSS - used if one single HTML page has a unique style.

<!DOCTYPE html>
<html>
<head>
<style>
body {
  background-color: yellow;
}

h1 {
  color: red;
  margin-left: 40px;
}
</style>
</head>
<body>

<h1>This is a heading</h1>
<p>This is a paragraph.</p>

</body>
</html>

3. Inline CSS - used to apply a unique style for a single element.

<!DOCTYPE html>
<html>
<body>

<h1 style="color:blue;text-align:center;">This is a heading</h1>
<p style="color:red;">This is a paragraph.</p>

</body>
</html>

CSS Comments

Comments are used to explain the code, and may help when you edit the source code at a later date.

/* This is a single-line comment */
p {
  color: red;
}
p {
  color: red;  /* Set text color to red */
}
/* This is
a multi-line
comment */

p {
  color: red;
}

CSS Colors

Colors are specified using predefined color names, or RGB, HEX, HSL, RGBA, HSLA values.

CSS Color Names

A color can be specified by using a predefined color name.

<h1 style="background-color:Orange;">Orange</h1>

CSS Background Color

Set the background color for HTML elements.

<p style="background-color:red;">Lorem ipsum...</p>

CSS Text Color

Set the color of text.

<p style="color:red;">Lorem ipsum...</p>

CSS Border Color

Set the color of borders.

<h1 style="border:2px solid Violet;">Hello World</h1>

CSS Color Values

Specified using RGB values, HEX values, HSL values, RGBA values, and HSLA values.

<h1 style="background-color:rgb(255, 99, 71);">...</h1>

RGB Value - a color can be specified as an RGB value, using this formula: rgb(red, green, blue).

background-color:rgb(255, 99, 71)

RGBA Value - RGBA color values are an extension of RGB color values with an alpha channel - which specifies the opacity for a color. An RGBA color value is specified with: rgba(red, green, blue, alpha).

background-color:rgba(255, 99, 71, 0.5)

HEX Value - a color can be specified using a hexadecimal value in the form.

background-color: #000000

3 Digit HEX Value - The 3-digit hex code is a shorthand for some 6-digit hex codes. The 3-digit hex code has the following form: #rgb

background-color:#fc9

HSL Value - a color can be specified using hue, saturation, and lightness (HSL) in the form: hsl(hue, saturation, lightness).

background-color:hsl(0, 100%, 50%)

HSLA Value - HSLA color values are an extension of HSL color values with an alpha channel - which specifies the opacity for a color. An HSLA color value is specified with: hsla(hue, saturation, lightness, alpha).

background-color:hsla(0, 100%, 50%, 0.5)

CSS Backgrounds

The CSS background properties are used to add background effects for elements.

CSS background-color - specifies the background color of an element.

body {
  background-color: lightblue;
}

Opacity / Transparency

opacity property specifies the opacity/transparency of an element. It can take a value from 0.0 - 1.0. The lower value, the more transparent.

div {
  background-color: green;
  opacity: 0.3;
}

Transparency using RGBA

If you do not want to apply opacity to child elements, like in our example above, use RGBA color values.

div {
  background: rgba(0, 128, 0, 0.3) /* Green background with 30% opacity */
}

CSS background-image - specifies an image to use as the background of an element.

body {
  background-image: url("paper.gif");
}

CSS background-repeat - repeats an image both horizontally and vertically.

body {
  background-image: url("gradient_bg.png");
  background-repeat: repeat-x;
}
body {
  background-image: url("gradient_bg.png");
  background-repeat: repeat-y;
}
body {
  background-image: url("gradient_bg.png");
  background-repeat: no-repeat;
}

CSS background-position - used to specify the position of the background image.

body {
  background-image: url("gradient_bg.png");
  background-repeat: no-repeat;
  background-position: right top;
}
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