position: fixed Misbehaving in Transformed Parents – Detailed Explanation

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Step 1: Understanding position: fixed

What is position: fixed?

• The fixed positioning in CSS anchors an element relative to the viewport.
• It does not move when scrolling.
• It is independent of the parent elements unless modified by special conditions.

Basic Example

.fixed-box {
    position: fixed;
    top: 20px;
    right: 20px;
    width: 100px;
    height: 100px;
    background: red;
}

✅ Expected Behavior:

• The .fixed-box remains in the same position even if the page scrolls.

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Step 2: The Problem – position: fixed Not Working Inside Transformed Parents

What Happens?

When a parent element has transform, position: fixed no longer behaves as expected.
Instead of staying fixed relative to the viewport, it acts as if it were positioned relative to the transformed parent.

Example of the Issue

.parent {
    position: relative;
    transform: scale(1); /* Creates a new stacking context */
    width: 300px;
    height: 300px;
    background: lightblue;
    overflow: hidden;
}

.fixed-box {
    position: fixed;
    bottom: 10px;
    right: 10px;
    width: 100px;
    height: 100px;
    background: red;
}

❌ Expected Behavior: The .fixed-box stays fixed in the viewport.
❌ Actual Behavior: The .fixed-box moves relative to .parent instead of the viewport.

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Step 3: Why Does This Happen?

When transform, perspective, or filter is applied to an element, it creates a new containing block instead of the default viewport behavior.

Key Concept: Containing Block

• Normally, position: fixed elements are relative to the viewport.
• However, a transformed parent becomes the new reference point for fixed elements inside it.

CSS Properties That Create a New Containing Block

Any of the following properties on a parent element override fixed positioning:

transform: scale(1); 
transform: rotate(0deg);
transform: translate(0);
perspective: 500px;
filter: blur(0);

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Step 4: How to Fix position: fixed Inside Transformed Parents

✅ Solution 1: Move the fixed Element Outside the Transformed Parent

Instead of placing the fixed element inside the transformed parent, move it outside in the DOM.

Fix Example

<div class="parent">
    <p>Transformed Parent</p>
</div>

<div class="fixed-box">I am Fixed</div> <!-- Moved outside -->

✅ This ensures fixed-box remains fixed relative to the viewport.

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✅ Solution 2: Use position: absolute Instead

If moving the element is not an option, use position: absolute and manually adjust the positioning.

Fix Example

.fixed-box {
    position: absolute; /* Instead of fixed */
    bottom: 10px;
    right: 10px;
}

✅ This makes the element behave correctly inside the transformed parent.

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✅ Solution 3: Use transform: none on the Parent

If you do not need the transform effect, simply remove it.

Fix Example

.parent {
    transform: none; /* Removes the containing block issue */
}

✅ This allows fixed positioning to behave normally.

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✅ Solution 4: Use will-change: transform on the Fixed Element

If the parent must remain transformed, applying will-change: transform to the fixed element can sometimes fix the issue.

Fix Example

.fixed-box {
    will-change: transform;
}

✅ This forces the browser to correctly calculate the fixed position.

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✅ Solution 5: Use top: calc(100vh - Xpx) Instead of bottom

Instead of using bottom, use calc() with vh (viewport height).

Fix Example

.fixed-box {
    position: absolute;
    top: calc(100vh - 50px); /* Positions it relative to viewport */
}

✅ This mimics fixed behavior without being affected by the parent.

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Step 5: Which Solution Should You Use?

Solution	Pros	Cons
Move the element outside the parent	Works best, keeps fixed behavior	Requires HTML structure change
Use position: absolute	Works within the parent	Not truly “fixed”
Remove transform from the parent	Restores normal fixed behavior	Might not be possible if transform is needed
Use will-change: transform on the fixed element	Works in some cases	Not always reliable
Use calc(100vh - Xpx) instead of bottom	Mimics fixed positioning	Not always precise

🚀 Best Practice: Move the fixed element outside the transformed parent whenever possible.

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Step 6: Debugging position: fixed Issues

1️⃣ Check if the Parent Has transform, perspective, or filter

1. Right-click on the element → Inspect Element.
2. Look in the Styles panel for:
   • transform
   • perspective
   • filter

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2️⃣ Use Chrome DevTools to Test Removing transform

1. Open Chrome DevTools (Right-click → Inspect).
2. Locate the parent element.
3. In the Styles panel, disable transform temporarily.
4. See if the fixed element behaves correctly.

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3️⃣ Test Alternative Positioning Strategies

• Try absolute positioning.
• Experiment with will-change: transform.
• Adjust top using calc(100vh - Xpx).

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Final Thoughts

• Why does position: fixed break? A transformed parent creates a new containing block.
• How to fix it? Move the element outside, use absolute, or remove transform.
• Best practice: Avoid placing fixed elements inside transformed parents.

By following these solutions, you can fix misbehaving position: fixed elements inside transformed parents!