What are some common CSS gotchas or bugs developers run into?
Jun 25, 2025 am 12:37 AM
The problem of element height collapse can be solved by setting overflow: hidden, using clearfix or using Flexbox instead; 2. Margin merge can be avoided by adding border, using inline-block or flex/grid layout; 3. The width of flex child elements does not take effect. Set min-width, flex-shrink: 0 or flex: 0 0 200px; 4. position: absolute Positioning abnormality requires checking whether the positioning mode is set for the ancestor element; 5. The image exceeds the container or the proportional distortion can be controlled by max-width, object-fit or background-size.
During CSS development, many problems seem simple, but if you don’t pay attention to details, it can easily make people get stuck. The following lists some "pits" and corresponding solutions that front-end developers often encounter.
1. Height Collapse
This is a problem that is prone to occur when there are only floating elements inside the block-level element. The height of the parent container may be displayed as 0, causing a layout to be malfunctioned.
reason:
The floating element is separated from the document stream and the parent container cannot correctly identify the actual height of its child elements.
Solution:
- Set
overflow: hidden - Using clearfix technology:
.clearfix::after { content: ""; display: table; clear: both; } - Or use Flexbox layout instead to avoid float
2. Margin Collapse
Two vertically adjacent block-level elements, margins between them may merge into one, resulting in a smaller spacing than expected.
Common Situations:
- margin-top merger of father-son relationship
- Merge up and down margin between adjacent brother elements
Coping methods:
- Add border or padding to the parent element
- Use inline-block instead of block layout
- Using flex or grid layout can avoid this problem
Although margin merge is a standard behavior, it is often not intuitive in actual development and requires special attention.
3. The width of the flex child element does not take effect
When you set display: flex container, the child element inside has width: 200px set, but finds that it has not taken effect.
Why?
Flex will allow child elements to scale to the container size by default.
Solution:
- Set
min-widthinstead of width - Add
flex-shrink: 0to disable compression - Identify
flex: 0 0 200px, that is, fixed size
This is especially important when making tables or card lists.
4. position: absolute does not position as expected
You set position: absolute for an element, but it does not position relative to the parent you expect.
Key points:
- It will keep looking up the most recent ancestor elements that have
position: relative、absolute、fixed 或sticky - If it cannot be found, keep finding the viewport or document root
suggestion:
- Check if the parent has set the correct positioning mode
- Sometimes adding
position: relativeis necessary - Using browser developer tools to view hierarchical relationships is easier to find problems
5. Pictures exceed container or proportional distortion
Pictures often have problems in responsive designs, such as breaking containers or deforming them.
Common practices:
img {
max-width: 100%;
height: auto;
}If you want the image to maintain proportion and fill the entire container, you can use:
img {
width: 100%;
height: 100%;
object-fit: cover;
} If it is a background image, remember to set background-size: cover or contain .
These problems may not seem big, but they often affect the overall layout and even functional performance. Some are CSS features, and some are browser default behavior. The key is to understand the principles and be familiar with common techniques. Basically, this is all. Pay more attention to the structure and style inheritance relationship during development, and you can take fewer pitfalls.
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