Opacity is causing issues with hover effects in CSS

Question

Opacity is causing issues with hover effects in CSS

I'm facing an unusual CSS challenge.

Check out this simple code snippet below that showcases the issue:

<html>
  <head>
     <style>
      .hover {
        float: right;
      }
      .hover:hover {
        background-color: blue;
      }
      .blocker {
        opacity: 0.5;
      }
    </style>
  </head>
  <body>
    <div class="hover">hover</div>
    <div class="blocker">blocker</div>
  </body>
</html>

I have a situation where div A is floating over another div B with an opacity of 0.5. I want to apply a CSS hover effect on the floating div. However, for some reason, it doesn't seem to work.

Changing the float direction from right to left doesn't make a difference.

Interestingly, when I increase the opacity to 1, the hover effect starts working suddenly.

Could someone shed light on why this behavior occurs?

To "solve" this issue, I can wrap the content of the blocker div in a span, but it seems unnecessary.

Feel free to view this problem in action on jsFiddle: http://jsfiddle.net/ed82z/1/

css hover opacity

Answer 1

Answer №1

To simplify, an element is considered "above" another if its opacity is less than 1.

The crucial concept here is a Stacking Context.

When the opacity is set to a value below one, it creates a new stacking context and is positioned under the element according to the specification.

This behavior can be found in float and opacity:

The root element acts as the root stacking context. Other stacking contexts are formed by any positioned element (including relatively positioned elements) with a computed 'z-index' other than 'auto'. Stacking contexts may not necessarily be related to containing blocks. In future CSS versions, additional properties may introduce stacking contexts, such as 'opacity' [CSS3COLOR].

Regarding opacity:

An element with an opacity lower than 1 is composited from a single off-screen image, preventing content outside of it from being layered between pieces of content within it based on z-order. For this reason, implementations must generate a new stacking context for any element with an opacity below 1. If an element with opacity less than 1 is unpositioned, the layer it forms will be painted within its parent stacking context at the same order as if it had a ‘z-index: 0’ and ‘opacity: 1’. When an element with less than 1 opacity is positioned, the ‘z-index’ property follows the rules outlined in [CSS21], where 'auto' is equivalent to ‘0’ due to always creating a new stacking context. Refer to section 9.9 and Appendix E of [CSS21] for further details on stacking contexts. These guidelines do not apply to SVG elements, as SVG operates on its rendering model ([SVG11], Chapter 3).

How to resolve this:

You can address this issue by setting pointer-events to none, check out this fiddle.

Answer 2

To simplify, an element is considered "above" another if its opacity is less than 1.

The crucial concept here is a Stacking Context.

When the opacity is set to a value below one, it creates a new stacking context and is positioned under the element according to the specification.

This behavior can be found in float and opacity:

The root element acts as the root stacking context. Other stacking contexts are formed by any positioned element (including relatively positioned elements) with a computed 'z-index' other than 'auto'. Stacking contexts may not necessarily be related to containing blocks. In future CSS versions, additional properties may introduce stacking contexts, such as 'opacity' [CSS3COLOR].

Regarding opacity:

An element with an opacity lower than 1 is composited from a single off-screen image, preventing content outside of it from being layered between pieces of content within it based on z-order. For this reason, implementations must generate a new stacking context for any element with an opacity below 1. If an element with opacity less than 1 is unpositioned, the layer it forms will be painted within its parent stacking context at the same order as if it had a ‘z-index: 0’ and ‘opacity: 1’. When an element with less than 1 opacity is positioned, the ‘z-index’ property follows the rules outlined in [CSS21], where 'auto' is equivalent to ‘0’ due to always creating a new stacking context. Refer to section 9.9 and Appendix E of [CSS21] for further details on stacking contexts. These guidelines do not apply to SVG elements, as SVG operates on its rendering model ([SVG11], Chapter 3).

How to resolve this:

You can address this issue by setting pointer-events to none, check out this fiddle.

Answer 3

Answer №2

To solve my issue, I found that adding overflow: hidden did the trick:

.blocker {
    opacity: 0.5;
    overflow:hidden;
}

Alternatively, you can also try this solution:

.blocker { 
        opacity: 0.5;
        position:relative; 
        z-index:-1;
}

(Credit to @Eyal Barta for suggesting this option)

Check out this JSFiddle for a demonstration

The reason behind needing these changes is because .blocker was overlapping another div, a behavior easily observed using tools like Firebug.

By adding opacity, you're introducing a "stacking context".

This happens as a result of specific properties of these DIVs that cause them to establish a stacking context.

In this scenario, it's triggered by

elements with an opacity value less than 1.

This action assigns a z-index to your div, altering the order in which it's rendered.

To learn more about stacking contexts, check out this resource

Answer 4

To solve my issue, I found that adding overflow: hidden did the trick:

.blocker {
    opacity: 0.5;
    overflow:hidden;
}

Alternatively, you can also try this solution:

.blocker { 
        opacity: 0.5;
        position:relative; 
        z-index:-1;
}

(Credit to @Eyal Barta for suggesting this option)

Check out this JSFiddle for a demonstration

The reason behind needing these changes is because .blocker was overlapping another div, a behavior easily observed using tools like Firebug.

By adding opacity, you're introducing a "stacking context".

This happens as a result of specific properties of these DIVs that cause them to establish a stacking context.

In this scenario, it's triggered by

elements with an opacity value less than 1.

This action assigns a z-index to your div, altering the order in which it's rendered.

To learn more about stacking contexts, check out this resource

Answer 5

Answer №3

The .blocker class is currently overlapping the .hover class due to the use of float:right;

.blocker {
    opacity: 0.5; 
    width:100px
}

To resolve this issue, you can either change the float:left property in the blocker class or set a fixed width of 100px for the div to prevent overlap.

Answer 6

The .blocker class is currently overlapping the .hover class due to the use of float:right;

.blocker {
    opacity: 0.5; 
    width:100px
}

To resolve this issue, you can either change the float:left property in the blocker class or set a fixed width of 100px for the div to prevent overlap.

Opacity is causing issues with hover effects in CSS

Answer №1

How to resolve this:

Answer №2

Answer №3

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