The Large, Small, and Dynamic Viewports
The Large, Small, and Dynamic Viewports 관련
There are some changes being made regarding viewport units. The additions — which are part of the CSS Values and Units Level 4 specification — define several viewport sizes: the Large, Small, and Dynamic Viewport.
Thanks to these additions we will finally be able to solve that “100vh in Safari on iOS” issue.
Update 2021.07.14
Some parts of this post have been rewritten to include the latest CSSWG changes (w3c/csswg-drafts) regarding these units.
Update 2021.07.23 🎉
The proposed changes have landed in the official spec by now. This post has been updated accordingly.
The Large, Small, and Dynamic Viewports
The CSSWG has defined several extra Viewport Sizes and accompanying Viewport-relative Units (spec), in addition to the already existing vw/vh/vmin/vmax ones.
The Large Viewport
The Large Viewport is the viewport sized assuming any UA interfaces (such as the address bar) that are dynamically expanded and retracted to be retracted. It has the l-prefix, so units are lvh / lvw / lvmin / lvmax.
Tips
100lvh stands for 100% of the large viewport height.
The Small Viewport
The Small Viewport is the viewport sized assuming any UA interfaces that are dynamically expanded and retracted to be expanded. It has the s-prefix, so units are svh / svw / svmin / svmax.
Tips
100svh stands for 100% of the small viewport height.
The Dynamic Viewport
The Dynamic Viewport is the viewport sized with dynamic consideration of any UA interfaces. It will automatically adjust itself in response to UA interface elements being shown or not: the value will be anything within the limits of 100lvh (maximum) and 100svh (minimum).
Its prefix is d, so the units are dvh / dvw / dvmin / dvmax.
👉
You’ll want these Dynamic Viewport Units to have a UI that auto-stretches as the UA interface changes. 100dvh will automatically adapt itself.
body {
height: 100dvh; /* ✅ Do this! */
}
But, why? Can’t we just use a workaround?
You might ask yourself why we can’t simply rely on this JS workaround (getify) or the CSS workaround shown below, instead of introducing all these new units.
body {
height: 100vh;
}
@supports (-webkit-touch-callout: none) {
body {
height: -webkit-fill-available; /* ❌ Don't do this! */
}
}
Whilst the workaround above does achieve what we want, it only results in “full viewport height” for body. This is because -webkit-fill-available stretches items out inside their enclosing element — here the viewport. For some deeply nested elements that wouldn’t work, as -webkit-fill-available applied on them will look at their parent element — not the viewport. With 100dvh we can easily achieve what we want.
Above that you can’t use -webkit-fill-available to size something “half the size of the enclosing element”, as you can’t use -webkit-fill-available within calc(), e.g. height: calc(-webkit-fill-available * 0.5) is invalid CSS. Even if this were to be allowed one day, we’d again run into the issues when wanting to size a deeply nested element relatively to the viewport (see paragraph above).
So yes, we definitely do need these new Viewport Units 🤩
The catch
As mentioned before these new proposed l*/s*/d* units are additions to the already existing vw/vh/vmin/vmax units. With this, the CSSWG chose to keep these “old” units ambiguous: vw/vh/vmin/vmax have no explicit definition, and it’s totally up to the UA (browser) to define how they behave. Some browsers will have vh behave like lvh (like the current Safari does), while other browsers can make vh behave like dvh.
What also is up to the UA to choose, is the behavior of the Dynamic Viewport. Some browsers may update its value immediately while the interface is changing, whereas other browsers may only update the value after the UI has transitioned … the spec is fine with both.
The UA is not required to animate the dynamic viewport-percentage units while expanding and retracting any relevant interfaces, and may instead calculate the units as if the relevant interface was fully expanded or retracted during the UI animation.
Above that things like on-screen keyboards are not taken into account. For that we have the upcoming Virtual Keyboard API (MicrosoftEdge/MSEdgeExplainers).
Going Logical
Additionally the spec now also defines logical units, and thus talks about vi/dvi/svi and vb/dvb/svb which are the inline and block size respectively of the large/dynamic/small viewport. A small but very welcome addition.
Browser Support
Note
Although this post was originally published in July 2021, the section below is constantly being updated. Last update: Nov 10, 2022.
Here is an up-to-date list of browser support for the lv*, sv*, and dv* Viewport Units:
Chromium (Blink)
✅ Available in Chrome 108 and up.
Firefox (Gecko)
✅ Available in Firefox 101 and up.
Safari (WebKit)
✅ Available in Safari 15.4 and up.
To stay up-to-date regarding browser support, you can follow these tracking issues:
- Blink/Chromium: Issue #1093055 – Fixed (Closed)
- Gecko/Firefox: Issue #1610815 – RESOLVED FIXED
- WebKit/Safari: Issue #219287 – RESOLVED FIXED
The pen below will indicate whether your browser supports CSS Dynamic Viewport Units or not:
In Closing
It feels great to see things finally move in this area I must say, as the reported WebKit bug about 100vh not being 100vh-as-we-expect-it-to-be dates back from 2015, and the relevant CSSWG Issue (w3c/csswg-drafts) from 2019. As a final consensus on these viewport additions has been reached, I hope that the upcoming Safari 15 — which alters the viewport extensively as you scroll up/down — will make work to include these additions on top of their already supported env(safe-area-inset-*) values (e.g. height: calc(100vh - env(safe-area-inset-bottom));).
To help spread the contents of this post, feel free to retweet the announcement tweet: