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Table of Contents
Opacity affects the whole element
It interacts with parent and child elements
Use cases where opacity shines
Opacity vs rgba/hsla
Home Web Front-end CSS Tutorial How does the opacity property work?

How does the opacity property work?

Jun 26, 2025 am 12:22 AM
css Opacity

Opacity is used in CSS to control the transparency of elements, with values ??0 to 1, 1 being completely opaque and 0 being completely transparent. It affects the entire element and all its content, including text and child elements. For example, setting opacity: 0.6 will make the overall element 60% transparent. If you only need to adjust the background transparency without affecting the text, you should use rgba or hsla colors. In addition, child elements cannot exceed the transparency limit of the parent element by setting a higher opacity value. Opacity is often used in UI design for fading, masking, dark mode and other effects, such as superimposing translucent layers to improve text readability. Choosing opacity or rgba/hsla depends on whether the visibility of the internal elements is required to be preserved.

How does the opacity property work?

Opacity in CSS controls how transparent or see-through an element appears. A value of 1 means the element is fully opaque, while a value of 0 makes it completely transparent — basically invisible, though still taking up space on the page. Values ??in between let you fine-tune the visibility, like 0.5 for 50% transparency.

Opacity affects the whole element

One important thing to understand: when you apply opacity to an element, it doesn't just affect the background or color — it impacts everything inside it , including text, borders, and child elements.

For example:

 .box {
  opacity: 0.6;
}

This will make the box background, any images inside it, and even the text all 60% transparent. If you only want part of an element to be transparent (like just the background), opacity might not be the best choice — you could use rgba or hsla colors instead.

It interacts with parent and child elements

If a parent element has opacity set, child elements can't be more opaque than their parent . So if you set a parent's opacity to 0.5 , even if a child has opacity: 1 , it won't override that — it'll still look at most 50% transparent.

This behavior can trip people up when trying to layer semi-transparent backgrounds with solid text or buttons.

Use cases where opacity shines

Opacity is useful in many UI scenarios, especially for subtle effects:

  • Fading out inactive elements (like dimming a card when hovered)
  • Creating overlays or dark modes with a slight tint
  • Showing loading states by reducing opacity of content

A common trick is using a semi-transparent overlay on top of images to improve text readability:

 <div class="image-wrapper">
  <img src="/static/imghw/default1.png"  data-src="photo.jpg"  class="lazy" alt="Background image">
  <div class="overlay">Some text</div>
</div>
 .overlay {
  opacity: 0.7;
  background-color: #000;
  color: white;
}

Opacity vs rgba/hsla

If you want to control only the background's transparency without affecting text or other content, consider using rgba() or hsla() for background colors instead of opacity:

 .background-only-transparency {
  background-color: rgba(0, 0, 0, 0.5); /* Black with 50% transparency */
}

This way, only the background is transparent — the text stays solid.

So when choosing between opacity and rgba , think about what exactly needs to be transparent and whether nested elements should remain unaffected.

Basically that's it.

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