In CSS, the order in which elements are drawn is affected by a variety of factors. By default, the browser draws in the order of positioning elements with z-index set in the background and border → text content → child elements. 1. The default drawing order is not entirely based on the DOM structure, but follows the painting order; 2. The hierarchy is determined by whether it belongs to the same stacking context, whether a new stacking context is created (such as transform, filter, opacity
In CSS, the paint order of elements is an important factor affecting the rendering effect of pages. Many people will find that sometimes even if the style is clearly written, some parts cannot be displayed, or are blocked by other content, which is often related to the drawing order.

In fact, when the browser draws a page, there are certain rules. Understanding these rules can help you control layout and hierarchical performance more accurately.
1. Default drawing order: draw from back to front
When the browser draws HTML elements by default, it does not draw them completely in the order from front to back of the DOM structure. It has its own set of "painting priorities", such as:

- Draw the background and border first
- Secondly text content
- Finally, the
z-index
positioning element is set in the sub-element
This order is part of the standard, called painting order , and you can find the complete process in the MDN or W3C documentation. Simply put, ordinary elements may not cover the positioning elements, even if they are written in HTML.
2. What determines the level? Not just z-index
When it comes to drawing order, many people's first reaction is z-index
, but it is only one factor and only works on positioning elements (such as position: relative
, absolute
, fixed
).

Factors that really affect hierarchy include:
- Whether the element belongs to the same stacking context (cascaded context)
- Whether properties such as
transform
,filter
,opacity are used, these will create a new cascaded context
-
z-index
value size (note that negative numbers are also valid)
For example, if you have two divs, one uses position: absolute
and z-index: 100
, and the other has no positioning but uses transform: translateX(0)
, then the latter may also appear above the former.
3. Tips to avoid drawing conflicts
To avoid the problems of styles covering each other and confusing levels, you can remember several practical suggestions:
- Try to avoid multiple elements using very high
z-index
values, which is easy to lose control. - Divide different stacking contexts for components or modules, such as using
transform
to create isolated environments - Use the debugging tool to view the hierarchy of elements, and the Layers panel of Chrome DevTools can see the actual drawing order
- If an element cannot be output, check whether the parent has truncated its draw range (such as
overflow: hidden
)
Basically that's it. The drawing order sounds a bit abstract, but it is very common in actual development, especially when doing animations, pop-ups, and complex interactions. Understanding how it works is much more efficient than simply trial and error.
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