In CSS, the z-index property is used to control the stacking order of elements that are positioned (i.e., elements with a position value of relative, absolute, or fixed). The z-index property specifies the stack level of an element and determines whether it will appear in front of or behind other elements. Elements with a higher z-index value will appear in front of elements with a lower z-index value.

Here’s an example of how you might use the z-index property:

.my-element {
    position: absolute;
    z-index: 1;
}

This would position the element with the class my-element and set its stack level to 1, which would cause it to appear in front of elements with a lower z-index value.

It’s important to note that the z-index property only works on elements that are positioned (i.e., elements with a position value of relative, absolute, or fixed). Elements with a position value of static (the default value) do not have a stack level and cannot be controlled with the z-index property.

You can also use the opacity property to control the transparency of an element. The opacity property specifies the transparency of an element, with a value of 0 being completely transparent and a value of 1 being completely opaque.

Here’s an example of how you might use the opacity property:

.my-element {
    opacity: 0.5;
}

This would make the element with the class my-element 50% transparent, which would allow elements behind it to show through.