@if conditional logic in SASS - Browser Rendering Trace

Render Flow - @if conditional logic

[Read SASS file] -> [Parse @if condition] -> [Evaluate condition] -> [Include matching CSS block] -> [Ignore other blocks] -> [Compile to CSS]

The SASS compiler reads the @if condition, checks if it is true or false, then includes only the CSS inside the true block in the final CSS output.

Render Steps - 3 Steps

Code Added:Basic box with width and height

Before

[ ] (empty space)

→

After

[________]
[        ]
[________]

The box element appears as a square with no background color, just empty space.

🔧 Browser Action:Creates box element with size, triggers layout

Code Sample

A square box that is red if $isRed is true, otherwise blue.

SASS

<div class="box">Hello</div>

SASS

$isRed: true;
.box {
  width: 10rem;
  height: 10rem;
  @if $isRed {
    background-color: red;
  } @else {
    background-color: blue;
  }
}

Render Quiz - 3 Questions

After applying step 2, what color is the box background?

A Blue

B Red

C No color

D Green

Common Confusions - 2 Topics

Why do I not see the styles from the @else block?

Because the @if condition was true, the compiler only includes the @if block styles and ignores the @else block. Only one block runs.

💡 Only one block of @if/@else runs based on the condition.

Can I use normal CSS properties inside @if?

Yes, you write normal CSS inside the @if block. The block is included or excluded entirely based on the condition.

💡 Think of @if as a gate that lets CSS in or keeps it out.

Property Reference

SASS Directive	Condition	Effect	Visual Result	Common Use
@if	True condition	Includes CSS inside block	Styles applied as expected	Apply styles conditionally
@else	Used after @if	Includes CSS if @if is false	Alternative styles applied	Fallback styles
@else if	Additional condition	Checks another condition if previous false	Conditional alternate styles	Multiple conditions

Concept Snapshot

@if conditional logic in SASS lets you include CSS only if a condition is true. Use @else for alternative styles if the condition is false. Only one block runs, so styles inside @if or @else appear, never both. This helps write dynamic styles based on variables or logic. Example: @if $isRed { background-color: red; } @else { background-color: blue; }