Bootstrap h-100 applied to or tag?

Question

In some cases, the Bootstrap class h-100 is applied to the <html> element, and in some cases to the <body> element, and sometimes to both. For example, in the code Sticky footer with fixed navbar, https://getbootstrap.com/docs/4.5/examples/sticky-footer-navbar/, the class h-100 is applied to both the <html> and <body> element, for short

<!doctype html>
<html lang="en" class="h-100">
<head>
...
</head>
<body class="d-flex flex-column h-100">
...
</body>
</html>

Are there any logic behind this, any rules to follow, when to address the <html> element, and when to address the <body> element?

Does this answer your question? [Make body have 100% of the browser height](https://stackoverflow.com/questions/6654958/make-body-have-100-of-the-browser-height) — Sergey Vyacheslavovich Brunov, Jun 24 '22 at 16:37

score 1 · Accepted Answer · edited Jun 24 '22 at 16:26

Overview

In general 100% height is required when the design requires full height.

As an example a typical situation is to position the footer on the bottom, regardless of the screen's height. While developing these design concepts, lacking 100% height shows clear issues when dealing with empty pages, where no content is generating height and as a result, the footer is stacked below the header.

Design concepts that introduce height requirements:

fixed footer
centered content vertically
modal UI backdrop
scrolling enhancements
…

These concepts usually only affect the CSS of your website and require the functionality to be both on the html and body tag.

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So the question remains, why only on the <html /> or only the <body />? My idea is it depends on certain JavaScript calculations.

Imagine you require the top position of an element => document object is used
Imagine you require to scroll to a certain position => window object is used

Both functionalities can work separately where document object finds elements in the <body /> and window object finds properties on the <html /> tag.

Not entirely certain it's split this way, but I can see someone adding h-100 class to the html tag to fix a scrolling issue and someone else adding h-100 to the body to fix an offset/position issue. In my opinion it's always better to introduce height 100% for both.

Bootstrap h-100 applied to or tag?

1 Answers1

Overview

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Linked