Z-index basics in CSS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the CSS property z-index control?

The z-index property controls the vertical stacking order of elements that overlap on a webpage. Higher values appear on top of lower values.

beginner

Which elements can have a z-index value applied?

Only elements with a position value other than static (like relative, absolute, fixed, or sticky) can have a z-index value applied.

intermediate

What happens if two overlapping elements have the same z-index value?

If two elements have the same z-index, the one that appears later in the HTML code will be displayed on top.

intermediate

Can z-index have negative values? What does it mean?

Yes, z-index can be negative. Negative values place the element behind elements with zero or positive z-index values.

advanced

What is a stacking context in relation to z-index?

A stacking context is a group of elements that have their own local stacking order. Elements inside a stacking context are stacked relative to each other, but the entire group stacks as one unit in the parent context.

Which CSS property must be set for z-index to work on an element?

A position

B display

C margin

D color

The position property must be set to relative, absolute, fixed, or sticky for z-index to take effect.

What does a higher z-index value mean?

A The element is smaller

B The element is further back

C The element is invisible

D The element is on top

A higher z-index means the element appears on top of elements with lower values.

If two elements overlap and have the same z-index, which one appears on top?

A The one with the higher <code>z-index</code>

B The one that appears first in the HTML

C The one that appears last in the HTML

D The one with the bigger size

The element that appears later in the HTML code is stacked on top if z-index values are equal.

Can z-index have negative values?

A No, only positive values are allowed

B Yes, negative values place elements behind others

C Yes, but negative values make elements invisible

D No, negative values cause errors

Negative z-index values place elements behind those with zero or positive values.

What is a stacking context?

A A group of elements stacked together with their own order

B A CSS property for colors

C A type of HTML tag

D A JavaScript function

A stacking context is a group of elements that stack together with their own local order, separate from the rest of the page.

Explain how z-index affects overlapping elements and what conditions must be met for it to work.

Think about how layers of paper stack and what makes one paper appear on top.

Describe what a stacking context is and why it matters when using z-index.

Imagine groups of stacked cards inside boxes stacked on a table.