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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteSet the background-size property on the element that owns the background-image. Use cover for an edge-to-edge hero or panel, contain when every part of the image must remain visible, or explicit lengths and percentages when you need a controlled rendered size.
.hero {
background-image: url("hero.jpg");
background-size: cover;
background-position: center;
background-repeat: no-repeat;
}cover preserves the image’s proportions but can crop an edge. contain preserves the complete image but can leave empty bands. The correct choice depends on whether coverage or complete visibility matters more.
What background-size controls
According to MDN Web Docs, background-size sets the size of an element’s background image. It does not resize an ordinary inline <img>; it applies to images supplied through background-image.
The property’s initial value is auto auto. You can provide a keyword, one size, or two sizes:
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| Value | Result | Use when |
|---|---|---|
cover |
Scales proportionally until the entire background positioning area is covered; one axis may be cropped. | You need a full-bleed hero, banner or section. |
contain |
Scales proportionally so the whole image fits inside the area; uncovered space may remain. | Every part of a logo, diagram or product image must show. |
300px or 50% |
Sets one dimension; the other remains auto and keeps the image ratio. |
You want a particular rendered width or height. |
300px 200px |
Sets width and height independently, which can distort the image. | The exact box is more important than natural proportions. |
auto |
Uses the image’s intrinsic dimension for that axis. | You are combining a fixed axis with natural sizing. |
Values can be combined for multiple background layers by separating each layer’s size with commas, in the same order as the corresponding background-image values.
Choose between cover and contain
Use cover to fill the element
cover scales the image until no part of the element’s background positioning area is uncovered. If the image and element have different aspect ratios, the excess is cropped. A centered, non-repeating hero usually starts with:
.hero {
min-height: 420px;
background: #172033 url("hero.jpg") center / cover no-repeat;
}The color is a fallback while the image loads and remains visible wherever the image does not cover an area or contains transparent pixels. Move the focal point with background-position:
.hero {
background-size: cover;
background-position: 65% center;
}
/* Keep the top of a portrait subject visible */
.portrait-hero {
background-position: center top;
}Use contain to show the whole image
contain fits the complete image inside the area while preserving its ratio. The remaining space shows the element’s background color. Set background-repeat: no-repeat or the image can tile into that space, as explained in MDN’s background resizing guide.
.diagram {
min-height: 360px;
background-color: #f3f5f7;
background-image: url("architecture.svg");
background-size: contain;
background-position: center;
background-repeat: no-repeat;
}Set an exact or responsive size
One value: preserve the ratio
With one length or percentage, that value sets the background width and the height is calculated automatically. For example:
.card {
background-image: url("texture.png");
background-size: 300px;
background-repeat: no-repeat;
}
.banner {
background-size: 50%;
background-repeat: no-repeat;
}A percentage is relative to the background positioning area, normally the padding box established by background-origin. It is not automatically the viewport width. With background-attachment: fixed, the reference area is the viewport. See MDN’s reference for these percentage rules.
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Two values: set width and height
.badge {
background-image: url("badge.png");
background-size: 120px 80px;
background-repeat: no-repeat;
}Independent dimensions can stretch the source. If distortion is unacceptable, use one value with auto, such as 120px auto, or use contain.
Responsive sizing with clamp()
CSS functions work as length values, so a background can grow between limits:
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.hero {
background-size: clamp(520px, 75vw, 1200px) auto;
background-position: center;
background-repeat: no-repeat;
}This is different from cover: the image has a bounded size and may leave uncovered space. Supply a background color for that space.
Build a complete full-page background
Apply the image to the element that should paint it. For a page-wide background, that is commonly body (or a dedicated wrapper):
html, body {
min-height: 100%;
}
body {
margin: 0;
color: white;
background-color: #101827;
background-image: url("site-background.jpg");
background-size: cover;
background-position: center;
background-repeat: no-repeat;
background-attachment: fixed;
}A fixed attachment uses the viewport as the reference area for percentage sizing. It can also behave differently on mobile browsers, so test scrolling on the devices your audience uses. If you do not need a viewport-fixed effect, omit background-attachment: fixed.
Combine layers, overlays and positioning
Multiple backgrounds are listed from front to back. Give each image its own size and position:
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.hero {
background-image:
linear-gradient(rgba(0, 0, 0, .45), rgba(0, 0, 0, .45)),
url("hero.jpg");
background-size: cover, cover;
background-position: center, center;
background-repeat: no-repeat, no-repeat;
}The gradient is a separate layer, so it needs a corresponding size and position. A shorthand form is valid when the slash separates position from size:
.hero {
background: #182235 url("hero.jpg") center / cover no-repeat;
}Keep important content from being cropped
- Identify the subject that must remain visible.
- Try
background-position, using keywords such astop,right, or percentages such as70% center. - Give the section a stable minimum height so responsive text does not unexpectedly change the crop.
- Use a different, wider or taller source image at a breakpoint if one composition cannot work at every ratio.
- Choose
containwhen cropping is unacceptable, and design the surrounding color or spacing for the resulting empty bands.
.hero {
min-height: 28rem;
background: #202a3a url("desktop-hero.jpg") center / cover no-repeat;
}
@media (max-width: 600px) {
.hero {
min-height: 34rem;
background-image: url("mobile-hero.jpg");
background-position: 60% center;
}
}Accessibility and loading considerations
A CSS background is decorative by default and has no alternative text. Do not put essential words, prices or instructions only in the image; place that information in HTML. If the image communicates meaningful content, an <img> with useful alt text is usually a better semantic choice.
Provide a background color that maintains readable contrast before the image is available and behind transparent pixels. A text overlay may need its own solid or translucent layer, as in the gradient example above.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot the common failures
The image does not change size
- Check that
background-sizeandbackground-imageare on the same element. - Confirm the element has dimensions. A block with no content, height or padding may have no visible area.
- Inspect computed styles for a later rule, inline style or shorthand declaration overriding your value.
contain produces a tiled pattern
Add background-repeat: no-repeat. Tiling is the default behavior when the fitted image does not cover the entire area.
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That cropping is expected when aspect ratios differ. Adjust background-position, change the source composition, or switch to contain if complete visibility is required.
A percentage looks unexpectedly large or small
Measure the element’s background positioning area rather than the viewport. Check padding and background-origin; also check whether background-attachment: fixed changes the reference area to the viewport.
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Transparent areas show the wrong color
Set background-color explicitly. The color is visible wherever the image is transparent or leaves uncovered space.
The image is stretched
You probably supplied two mismatched dimensions, such as 300px 200px for a source with another ratio. Use auto for one axis, one size value, cover, or contain.
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Quick decision guide
- Choose
coverfor edge-to-edge visual impact. - Choose
containplusno-repeatwhen the complete image matters. - Choose one length or percentage for proportional custom sizing.
- Choose two values only when you accept possible distortion.
- Use
background-position, responsive source images and a fallback color to control the result.
Frequently Asked Questions
Can I use background-size with several background images?
Yes. Separate each layer’s size with commas and keep the order aligned with the comma-separated background-image layers.
Is cover the same as stretching an image?
No. cover preserves the image ratio and crops the excess; it does not independently stretch width and height.
Why is an img element unaffected by my rule?
background-size applies only to CSS background images. Resize an img with its own width, height and object-fit rules.
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