Increase size of h6 class to more clearly be a heading

[willfaught]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

When used as the only heading level in a page, the h6 class appears to be just another paragraph. This causes confusion. Perhaps it would be less surprising if the h6 class appeared bigger than paragraph text.

Motivation and context

See willfaught/paige#104

[mdo]

The browser defaults are even smaller fwiw. Unsure how much I want to revisit here, but maybe a 1.125rem in like v5.4.0 or later at best?

[Jackkk123]

To enhance the visual hierarchy while maintaining the Bootstrap design system, I suggest:

1. Increasing h6 font-size from 0.85rem to 1.125rem
2. Adding slight font-weight enhancement (500 or semi-bold)
3. Implementing complementary margin adjustments to maintain vertical rhythm

[dailytabs]

I disagree. Having the final heading being the same as normal text is very common. IAC, should be using fs-* and customizing them. Additionally, changing this in a .x does not sound like a good idea.

[julien-deramond]

I’m not surprised by the current Bootstrap rendering, but I don’t have a particularly strong opinion on it either.

Bootstrap already provides a solid set of utilities and customization options that make it easy to override default styles. Developers can apply custom classes, use utility classes for things like spacing or text styling, and even redefine Sass variables to ensure consistent, project-specific designs.

That said, in some tools or plugins, Bootstrap’s CSS may be applied automatically to Markdown content without an easy way to override the rendering. In those cases, it’s important that headers have some visual distinction from normal text. Font size is one option, but not the only one—other styling cues like boldness, color, or spacing can also help. Interestingly, if I remember correctly, in tools like Microsoft Word, the equivalent of <h6> is sometimes smaller than body text, but is still visually distinct thanks to its different texture or style.

However, IMHO, if any changes were to be made to the default header styling, they should be introduced in a major version update. Headers and their related utilities are deeply integrated into many existing projects, and modifying them could cause widespread issues. Even with Bootstrap’s flexibility, changing default behavior can lead to unexpected side effects or require significant effort to adapt.

For context, here’s how Markdown rendered with Primer styles looks:

---

# h1
Normal text

## h2
Normal text

### h3
Normal text

#### h4
Normal text

##### h5
Normal text

###### h6
Normal text

h1

Normal text

h2

Normal text

h3

Normal text

h4

Normal text

h5

Normal text

h6

Normal text

[mdo]

Closing for now, we can revisit in v6 if we want.

[willfaught]

@mdo Why not move this to a v6 milestone instead of closing it? I see you’re working on v6 right now.