Create a slide with a content box

Oct 13, 2025 by wbrum.org 31 views

Introduction

When creating presentations with positioned content boxes using Reveal.js, there's an inconsistency in how content is displayed across different screen sizes. Specifically, when the browser window is maximized, the upper portion of text content becomes cut off or invisible. This behavior suggests a potential issue with how Reveal.js handles absolute positioning in responsive contexts.

Reproduction Steps

To reproduce this issue, follow these steps:

Create a slide with a content box: Use Reveal.js to create a slide with a content box that uses absolute positioning with percentage-based values.
Position the content: Position the content using top percentage values (e.g., top: 50%) and use transform: translate(-50%, -50%) for centering.
View the presentation: View the presentation in a maximized browser window.
Resize the browser window: Resize the browser window to be smaller.
Notice the difference: Notice the difference in content visibility between the two states.

Expected Behavior

Content positioned with absolute positioning should be consistently visible regardless of browser window size. Elements positioned with percentage-based values should scale proportionally while maintaining their visibility.

Actual Behavior

Content is fully visible when the browser window is smaller, but when maximized, the upper portion of content becomes cut off or entirely invisible.

Attempted Solutions

Several solutions were attempted to resolve this issue:

Solution 1: Using `bottom` instead of `top` positioning

.content-box {
    position: absolute;
    bottom: 50px;
    left: 50%;
    transform: translateX(-50%);
    /* other styles */
}

Result: This caused all content to completely disappear, with only fixed position elements like the "AI-Powered Assistant" label remaining visible.

Solution 2: Using adjusted `top` percentages with modified transform

.content-box {
    position: absolute;
    top: 75%;
    left: 50%;
    transform: translate(-50%, 0);
    /* other styles */
}

Result: This solution worked correctly, showing that Reveal.js has compatibility issues with certain positioning approaches.

Solution 3: Adding responsive adjustments

@media (max-height: 700px) {
    .content-box {
        top: 70%;
    }
}

@media (max-height: 500px) {
    .content-box {
        top: 65%;
    }
}

Technical Details

Reveal.js version: Clone on 2025/03/14
Browser: Chrome Version 134.0.6998.89 (Official Build) (64-bit)
OS: Windows 11 (64-bit)

Conclusion

There appears to be an incompatibility between Reveal.js's presentation rendering and certain CSS positioning techniques, particularly:

Bottom-based positioning (bottom: Npx) causes elements to disappear completely
Default top-based positioning with vertical centering (top: 50%, transform: translate(-50%, -50%)) causes content to be cut off in maximized browser windows

The workaround is to use top-based positioning with a higher percentage value and remove the vertical transform component:

top: 75%;
transform: translate(-50%, 0);

This issue affects the creation of responsive presentations and requires developers to use specific positioning techniques that may not be intuitive.

Recommendations

To avoid this issue, developers should:

Use top-based positioning with a higher percentage value: Instead of using top: 50%, use top: 75% or higher.
Remove the vertical transform component: Remove the transform: translate(-50%, -50%) component to avoid centering issues.
Use responsive adjustments: Use media queries to adjust the positioning of elements based on screen size.

Introduction

In our previous article, we discussed the content positioning inconsistency in Reveal.js across different screen sizes. We explored the reproduction steps, expected behavior, actual behavior, and attempted solutions to resolve this issue. In this article, we'll answer some frequently asked questions (FAQs) related to this topic.

Q: What is the root cause of the content positioning inconsistency in Reveal.js?

A: The root cause of the content positioning inconsistency in Reveal.js is the incompatibility between Reveal.js's presentation rendering and certain CSS positioning techniques, particularly bottom-based positioning and default top-based positioning with vertical centering.

Q: Why does bottom-based positioning cause elements to disappear completely?

A: Bottom-based positioning causes elements to disappear completely because Reveal.js's presentation rendering does not support this type of positioning. When you use bottom: Npx, the element is positioned at the bottom of the parent element, but Reveal.js does not account for this positioning, resulting in the element disappearing.

Q: Why does default top-based positioning with vertical centering cause content to be cut off in maximized browser windows?

A: Default top-based positioning with vertical centering causes content to be cut off in maximized browser windows because Reveal.js's presentation rendering does not support this type of positioning. When you use top: 50% and transform: translate(-50%, -50%), the element is centered vertically, but Reveal.js does not account for this positioning, resulting in the content being cut off.

Q: What is the workaround for this issue?

A: The workaround for this issue is to use top-based positioning with a higher percentage value and remove the vertical transform component. For example, you can use top: 75% and transform: translate(-50%, 0) to position the element correctly.

Q: How can I avoid this issue in my Reveal.js presentations?

A: To avoid this issue in your Reveal.js presentations, you can follow these best practices:

Use top-based positioning with a higher percentage value: Instead of using top: 50%, use top: 75% or higher.
Remove the vertical transform component: Remove the transform: translate(-50%, -50%) component to avoid centering issues.
Use responsive adjustments: Use media queries to adjust the positioning of elements based on screen size.

Q: Can I use other CSS positioning techniques to avoid this issue?

A: Yes, you can use other CSS positioning techniques to avoid this issue. For example, you can use position: relative or position: fixed to position elements correctly. However, keep in mind that these techniques may have different effects on your presentation's layout and design.

Q: Is this issue specific to Reveal.js or can it occur in other presentation software?

A: This issue is specific to Reveal.js, but it can occur in other presentation software that uses similar CSS positioning techniques. However, the specific behavior and workarounds may vary depending on the software and its rendering engine.

Q: How can I report this issue to the Reveal.js developers?

A: If you encounter this issue, you can report it to the Reveal.js developers by creating a new issue on the Reveal.js GitHub repository. Provide a clear and concise description of the issue, including any relevant code snippets and screenshots. This will help the developers to reproduce and fix the issue.