CSS and its Syntax

CSS stands for Cascading Style Sheets.
It controls the visual presentation (style, layout, color, fonts, spacing, etc.) of HTML elements.

Why Use CSS?

Without CSS:

<h1>Hello</h1>

With CSS:

<h1 style="color: blue; font-family: Arial;">Hello</h1>

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3 Ways to Add CSS

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CSS Syntax

selector {
  property: value;
}

✅ Example:

h1 {
  color: blue;
  font-size: 24px;
}

This means make all <h1> elements blue and 24px in size.

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CSS Selectors

Selectors target which elements to style.

🔹 1. Universal Selector (*)

Targets all elements.

* {
  margin: 0;
  padding: 0;
}

---

🔹 2. Element Selector

Targets a specific HTML tag.

p {
  color: green;
}

---

🔹 3. Class Selector (.)

Targets elements with a specific class.

<p class="highlight">Hello</p>

.highlight {
  background-color: yellow;
}

---

🔹 4. ID Selector (#)

Targets an element with a unique ID.

<h1 id="main-title">Welcome</h1>

#main-title {
  font-size: 30px;
}

---

🔹 5. Group Selector

Style multiple elements at once.

h1, h2, p {
  font-family: Arial;
}

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🔹 6. Descendant Selector

Select elements inside other elements.

article p {
  color: gray;
}

Applies to all <p> inside <article>.

---

🔹 7. Child Selector (>)

Selects direct children only.

ul > li {
  list-style-type: square;
}

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Specificity (Which Style Wins?)

1. Inline style

2. Internal style

3. External style

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CSS Comment

CSS comments are lines of text that are ignored by the browser. They're used to explain code, leave notes, or temporarily disable CSS rules during development.

✅ Syntax:

/* This is a CSS comment */

• Comments start with /* and end with */.

• They can span multiple lines.

📌 Examples:

/* This sets the background color of the body */
body {
  background-color: #f0f0f0;
}

/*
  This section styles the navigation bar.
  It includes padding and font color.
*/
nav {
  padding: 10px;
  color: white;
}

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CSS Colors

✅ 1. Color Names

CSS supports 147 predefined color names, like:

color: red;
color: blue;
color: lightgreen;
color: darkslategray;

Easy to use, but limited flexibility.

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✅ 2. HEX (Hexadecimal) Color

HEX is a base-16 value that defines red, green, and blue (RGB) using 2 hex digits each.

color: #RRGGBB;

• #FF0000 → red

• #00FF00 → green

• #0000FF → blue

• #FFFFFF → white

• #000000 → black

Short form also works: #FFF (same as #FFFFFF)

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✅ 3. RGB (Red, Green, Blue)

Each color is defined using integer values (0–255) for red, green, and blue:

color: rgb(255, 0, 0);    /* Red */
color: rgb(0, 255, 0);    /* Green */
color: rgb(0, 0, 255);    /* Blue */

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✅ 4. RGBA (RGB + Alpha Transparency)

Same as rgb(), but adds alpha (opacity) as a value from 0 (transparent) to 1 (opaque):

color: rgba(255, 0, 0, 0.5);   /* Semi-transparent red */

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CSS Background

The background property in CSS is used to set the background effects for elements. It can control background color, images, repeat behavior, positioning, and more.

✅ 1. background-color

Sets the background color of an element.

background-color: lightblue;

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✅ 2. background-image

Sets a background image using a URL.

background-image: url("image.jpg");

📌 Can be used with gradients too:

background-image: linear-gradient(to right, red, yellow);

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✅ 3. background-repeat

Controls if/how the image repeats.

background-repeat: repeat;        /* Default */
background-repeat: no-repeat;     /* Show once */
background-repeat: repeat-x;      /* Horizontal only */
background-repeat: repeat-y;      /* Vertical only */

---

✅ 4. background-position

Sets the starting position of the background image.

background-position: center;
background-position: top right;
background-position: 50% 50%;

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✅ 5. background-attachment

Defines whether the background scrolls with the page.

background-attachment: scroll;   /* Default */
background-attachment: fixed;    /* Stays in place */

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✅ 6. background (Shorthand)

You can combine all background properties in a single line:

background: url("bg.jpg") no-repeat center/cover fixed;

Format:

background: [color] [image] [repeat] [position]/[size] [attachment];

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CSS Units

CSS Units – Absolute & Relative

✅ Absolute Units

These units are fixed and do not scale with screen size or parent elements. Best for print or very controlled layouts.

Use Case: Print styles, very specific layouts.

✅ Relative Units

These units scale depending on parent elements or the viewport. Best for responsive web design.

Use Case: Responsive layouts, scaling text, flexible designs.

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✅ Quick Comparison:

Example:

html {
  font-size: 16px; /* 1rem = 16px */
}

.container {
  width: 80vw;
  padding: 2em;
  font-size: 1.2rem;
}

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CSS Fonts

The font properties in CSS let you control the style, size, weight, family, and more for the text on your web page.

✅ 1. font-family

Specifies the typeface (the font). Always provide fallback fonts.

font-family: 'Roboto', Arial, sans-serif;

• Custom font: 'Roboto' (loaded via @font-face or Google Fonts)

• Fallback: Arial

• Generic family: sans-serif

🎯 Common generic families:

• serif – like Times New Roman

• sans-serif – like Arial

• monospace – like Courier

• cursive, fantasy, system-ui

✅ 2. font-size

Defines the size of the text.

font-size: 16px;
font-size: 1.2em;
font-size: 2rem;

Relative units (em, rem, %) make your text responsive.

✅ 3. font-weight

Controls the boldness of the font.

font-weight: normal;     /* 400 */
font-weight: bold;       /* 700 */
font-weight: 100–900;    /* Numeric scale */

✅ 4. font-style

Defines the style (italic or normal).

font-style: normal;
font-style: italic;
font-style: oblique;

✅ 5. font-variant

Used for small caps:

font-variant: small-caps;

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CSS Text

These properties help you control the appearance and layout of text, including alignment, spacing, decoration, and transformation.

✅ 1. color

Sets the text color.

color: red;
color: #333;
color: rgb(255, 0, 0);

✅ 2. text-align

Aligns the text horizontally.

text-align: left;     /* Default */
text-align: right;
text-align: center;
text-align: justify;

✅ 3. text-decoration

Adds decorations like underline, line-through, etc.

text-decoration: none;
text-decoration: underline;
text-decoration: line-through;
text-decoration: overline;

Combine with color:

text-decoration: underline red;

✅ 4. text-transform

Changes the case of the text.

text-transform: none;
text-transform: uppercase;
text-transform: lowercase;
text-transform: capitalize;

✅ 5. letter-spacing

Adjusts space between characters.

letter-spacing: 2px;

✅ 6. word-spacing

Adjusts space between words.

word-spacing: 5px;

✅ 7. line-height

Controls space between lines of text.

line-height: 1.5;

✅ 8. Text Shadow

Adds shadow to text.

text-shadow: 2px 2px 5px gray;

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What is box-sizing in CSS?

The box-sizing property defines how the total width and height of an element is calculated — whether or not it includes padding and border.

By Default (content-box):

box-sizing: content-box;

• Only the content is counted in the width and height.

• Padding and border are added outside the defined width/height.

Example:

width: 300px;
padding: 20px;
border: 10px solid black;

Total width = 300 + 20*2 + 10*2 = 360px
Total height = same calculation

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✅ box-sizing: border-box;

box-sizing: border-box;

• The width and height include content + padding + border.

• No need to manually calculate extra space.

Example:

width: 300px;
padding: 20px;
border: 10px solid black;

Here, total width stays 300px.
Content area is automatically shrunk to fit the padding and border.

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📌 Why Use border-box?

• Keeps layout simple and predictable ✅

• Prevents overflow and alignment issues ✅

• Widely used in modern CSS frameworks ✅

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Best Practice (Set Globally):

* {
  box-sizing: border-box;
}

This sets all elements (including pseudo-elements) to calculate width and height in a consistent, easier-to-manage way.

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Box Model

The CSS box model is essentially a box that wraps around every HTML element. It consists of: content, padding, borders and margins.

In CSS, the term "box model" is used when talking about design and layout.

• Content - The content of the box, where text and images appear

• Padding - Clears an area around the content. The padding is transparent

• Border - A border that goes around the padding and content

Margin - Clears an area outside the border. The margin is transparent

🔹 1. Content Area

• Controls the actual content's dimensions.

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🔹 2. Padding Area

• Space between content and border.

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🔹 3. Border Area

• The visible edge surrounding padding and content.

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🔹 4. Margin Area

• Space outside the border, between this element and others.

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🔹 5. Box Behavior / Control

• Properties that influence how the box behaves.

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✅ Box Model Shorthand Example

.box {
  width: 200px;
  height: 150px;
  padding: 20px;
  margin: 10px;
  border: 2px solid black;
  box-sizing: border-box;
}

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Display in CSS

The display property specifies the display behavior (the type of rendering box) of an element.

✅ block

• Takes up 100% width of the parent (whole line).

• Always starts on a new line.

• You can set width and height.

Example elements: <div>, <p>, <h1>

p {
  display: block;
}

Makes the paragraph take full width and start on a new line.

✅ inline

• Takes up only as much width as needed.

• Sits side by side with other inline elements.

• You cannot set width or height.

Example elements: <span>, <a>, <strong>

a {
  display: inline;
}

Makes the anchor behave like text — no line break, no width/height control.

✅ inline-block

• Behaves like inline (sits next to others).

• But you can set width and height.

Best of both inline and block.

button {
  display: inline-block;
  width: 150px;
  height: 40px;
}

Button stays inline with others but can have a set width and height.

Common Use Cases

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CSS Gradients

Gradients let you transition between two or more colors smoothly — and they're generated by the browser, so no image files needed!

✅ 1. Linear Gradient

Color changes in a straight line (top to bottom by default).

background: linear-gradient(direction, color1, color2, ...);

Examples:

background: linear-gradient(to right, red, blue);
/* From left to right */

background: linear-gradient(to bottom right, #ff7e5f, #feb47b);
/* Diagonal gradient */

background: linear-gradient(45deg, #00c6ff, #0072ff);
/* Using degree */

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✅ 2. Radial Gradient

Color radiates outward from a central point (like a circle or ellipse).

background: radial-gradient(shape size at position, color1, color2, ...);

Examples:

background: radial-gradient(circle, red, yellow, green);

background: radial-gradient(ellipse at center, #ff9a9e, #fad0c4);

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Box Shadow & Drop Shadow

1. box-shadow (for elements)

Adds shadow around the border of an element — often used to create depth or elevation.

✅ Syntax:

box-shadow: offset-x offset-y blur-radius spread-radius color;

• offset-x → Horizontal position (right if positive, left if negative)

• offset-y → Vertical position (down if positive, up if negative)

• blur-radius (optional) → Soften the edges

• spread-radius (optional) → Expand or shrink the shadow

• color → Shadow color

Example:

box-shadow: 5px 5px 15px rgba(0, 0, 0, 0.3);

Multiple Shadows:

You can stack shadows with commas:

box-shadow: 2px 2px 4px red, -2px -2px 4px blue;

Inset Shadow:

To apply shadow inside the element:

box-shadow: inset 2px 2px 5px rgba(0,0,0,0.5);

2. filter: drop-shadow() (for images, SVGs, elements)

drop-shadow() is part of the filter property and applies a shadow to the visual content (not the box), useful especially for transparent images, text, or SVGs.

✅ Syntax:

filter: drop-shadow(offset-x offset-y blur-radius color);

No spread-radius, but it respects transparent areas of PNGs or SVGs!

Example:

filter: drop-shadow(4px 4px 6px rgba(0,0,0,0.5));

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Key Differences

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List in CSS

Used to style HTML lists (<ul>, <ol>, <li>).

✅ 1. list-style-type

Defines the type of marker (bullet or number) for list items.

ul {
  list-style-type: circle;
}

Common values:

• disc (default bullet)

• circle

• square

• decimal (numbers for <ol>)

• none (no bullet)

✅ 2. list-style-position

Sets where the marker appears — inside or outside the list item's content.

ul {
  list-style-position: inside;
}

• outside (default) — bullet is outside the content box

• inside — bullet is inside the content box

✅ 3. list-style-image

Replaces the default marker with a custom image.

ul {
  list-style-image: url('bullet.png');
}

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Anchor Link States (Pseudo-classes)

Anchor tags (<a>) have 4 main states, often remembered as LVHA:

✅ 1. :link

• Unvisited link (default state)

a:link {
  color: blue;
}

✅ 2. :visited

• Link that the user has already clicked

a:visited {
  color: purple;
}

✅ 3. :hover

• When the user hovers over the link

a:hover {
  text-decoration: underline;
  color: red;
}

✅ 4. :active

• When the link is being clicked (mouse down)

a:active {
  color: orange;
}

Order Matters!

Always use this order:

a:link
a:visited
a:hover
a:active

(LVHA – Link, Visited, Hover, Active)

Otherwise, some states might not work as expected.

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Pseudo Elements in CSS

1. ::before

• Inserts content before the element’s actual content.

h1::before {
  content: "🔥 ";
}

2. ::after

• Inserts content after the element’s content.

h1::after {
  content: " ✨";
}

You must use content: with ::before and ::after.

3. ::first-letter

• Styles the first letter of a block of text.

p::first-letter {
  font-size: 2rem;
  color: red;
}

4. ::first-line

• Styles the first line of text in a block (depends on screen width).

p::first-line {
  font-weight: bold;
}

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Position in CSS

The position property defines how an element is positioned in the document flow.

1. static (default)

• Normal document flow

• You can’t use top, right, bottom, left

• Used when no special positioning is needed.

• Most HTML elements are static by default.

📌 Use when: You don’t need to move the element manually.

div {
  position: static;
}

2. relative

• Element stays in its normal position

• You can move it with top, left, etc. relative to itself

• Use when you want to move an element slightly from its normal position.

• Can also be used as a reference for absolute children.

📌 Use when:

• You want to nudge an element without breaking layout.

• You want to position a tooltip or badge over a parent element.

Tip: Combine with z-index to bring things forward or behind.

div {
  position: relative;
  top: 10px;
  left: 20px;
}

3. absolute

• Removed from normal flow

• Positioned relative to the nearest positioned ancestor

• If no positioned ancestor → relative to <html> or body

• Use when you want to place something at a precise position.

• It removes the element from the normal layout.

📌 Use when:

• Creating dropdown menus.

• Positioning tooltips or popups.

• Designing modal dialogs or floating boxes.

💡 Needs a parent with position: relative or it will stick to the <body>.

div {
  position: absolute;
  top: 0;
  left: 0;
}

4. fixed

• Stays in one place even when scrolling

• Positioned relative to the viewport

• Use to pin an element to a specific spot on the screen — even when scrolling.

📌 Use when:

• You want a floating button (like a chat icon).

• Creating sticky footers/headers that never move.

• Displaying persistent alerts or banners.

div {
  position: fixed;
  bottom: 10px;
  right: 10px;
}

5. sticky

• Switches between relative and fixed based on scroll

• Sticks to a position when a threshold is reached

• Use to make elements stick temporarily while scrolling, then release.

📌 Use when:

• Creating sticky headers or section titles.

• Sidebar menus that scroll with the content up to a point.

💡 Needs a top, left, or bottom value and scrollable parent.

div {
  position: sticky;
  top: 0;
}

CSS z-index Property

• Controls the stacking order of elements

• Higher z-index = placed on top

• Works only with positioned elements (relative, absolute, fixed, sticky)

• Use when elements overlap and you want to control which one appears on top.

📌 Use when:

• Creating modals, popups, or tooltips.

• Fixing dropdown menus behind other elements.

• Overlapping images or buttons.

🔢 Higher z-index means it sits on top.

div {
  position: absolute;
  z-index: 10;
}

Example:

.box1 {
  z-index: 1;
}
.box2 {
  z-index: 2;
}

box2 will appear above box1.

Summary Table

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Flex Box -

Flexbox (Flexible Box) is a one-dimensional layout system that helps you align and distribute space among items in a single direction—either row or column.

Basic Terminology

• Flex Container: The parent element with display: flex.

• Flex Items: The child elements inside the flex container.

Enabling Flex

<div class="flex-container">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
</div>

.flex-container {
  display: flex;
  background-color: #ddd;
}

.item {
  background-color: #4CAF50;
  color: white;
  padding: 20px;
  margin: 5px;
}

Main Axis vs Cross Axis

• Main Axis = direction of flex (default: row → horizontal)

• Cross Axis = perpendicular to main axis

Common Properties on Container

1. flex-direction

Controls main axis direction.

.flex-container {
  display: flex;
  flex-direction: row; /* default */
}

Other options:

• row-reverse

• column

• column-reverse

---

2. justify-content

Aligns items on the main axis.

.flex-container {
  justify-content: center;
}

Other options:

• flex-start

• flex-end

• space-between

• space-around

• space-evenly

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3. align-items

Aligns items on the cross axis.

cssCopyEdit.flex-container {
  align-items: center;
}

Options:

• flex-start

• flex-end

• stretch

• baseline

---

4. flex-wrap

Makes items wrap to next line.

.flex-container {
  flex-wrap: wrap;
}

Properties on Flex Items

1. flex

Shorthand for flex-grow, flex-shrink, flex-basis.

.item {
  flex: 1;
}

✅ Makes all items share available space equally.

---

2. order

Controls display order.

.item {
  order: 2;
}

Key Flexbox Use Cases

✅ Navigation bars
✅ Centering elements
✅ Equal height columns

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GRID

CSS Grid is a two-dimensional layout system for building complex layouts with rows and columns.

Basic Terminology

• Grid Container: Parent with display: grid

• Grid Items: Children of grid container

Enabling Grid

<div class="grid-container">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
  <div class="item">4</div>
</div>

.grid-container {
  display: grid;
  grid-template-columns: 100px 100px;
  grid-template-rows: 100px 100px;
  gap: 10px;
}

.item {
  background-color: #2196F3;
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
}

✅ Result: 2x2 grid with 10px gaps.

---

✅ Define Columns with grid-template-columns

grid-template-columns: 1fr 2fr;

• fr = fraction of available space

---

✅ Define Rows

grid-template-rows: 100px 200px;

---

✅ gap

Space between grid cells.

gap: 20px;

---

✅ Placing Items

.item1 {
  grid-column: 1 / 3;
}

✅ Makes item span 2 columns.

Key Grid Use Cases

✅ Page layouts
✅ Photo galleries
✅ Complex, two-dimensional designs

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CSS Animation

Animation in CSS allows elements to move, change color, grow/shrink, rotate, and more — without JavaScript.

Two Ways to Animate in CSS

1. Transitions – Simple changes between two states (hover, focus, etc.)

2. Animations – More control, keyframes, multiple steps

CSS TRANSITIONS

A transition is used to animate properties smoothly when they change (e.g., width, background, transform, etc.)

Example: Button Hover

<!DOCTYPE html>
<html>
<head>
  <style>
  div {
  width: 100px;
  height: 100px;
  background: red;
  transition: width 2s;
}

div:hover {
  width: 300px;
}
  </style>
</head>
<body>
       <div></div>
</body>
</html>

Common timing functions: ease, linear, ease-in, ease-out

linear - Same speed throughout

ease - Slow start → Fast middle → Slow end

ease-in - Slow start → Fast end

ease-out - Slow end

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CSS ANIMATIONS

CSS @keyframes define how an element will animate step-by-step.

Example: Bouncing Ball

<!DOCTYPE html>
<html>
<head>
  <style>
    .ball {
      width: 50px;
      height: 50px;
      background-color: red;
      border-radius: 50%;
      position: relative;
      animation: bounce 1s infinite;
    }

    @keyframes bounce {
      0%   { top: 0; }
      50%  { top: 100px; }
      100% { top: 0; }
    }
  </style>
</head>
<body>
  <div class="ball"></div>
</body>
</html>

• animation-name, animation-duration, animation-iteration-count, animation-timing-function

• infinite = keeps repeating

Animation Properties

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Example: Fading Text In and Out

<!DOCTYPE html>
<html>
<head>
  <style>
    .fade {
      font-size: 24px;
      animation: fadeinout 2s infinite;
    }

    @keyframes fadeinout {
      0%   { opacity: 0; }
      50%  { opacity: 1; }
      100% { opacity: 0; }
    }
  </style>
</head>
<body>
  <p class="fade">I fade in and out!</p>
</body>
</html>