CSS is about styling bins. Actually, the entire internet is product of bins, from the browser viewport to components on a web page. However each occasionally a brand new function comes alongside that makes us rethink our design method.
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Spherical shows, for instance, make it enjoyable to play with round clip areas. Cellular display screen notches and digital keyboards supply challenges to greatest arrange content material that stays away from them. And twin display screen or foldable gadgets make us rethink tips on how to greatest use out there area in quite a lot of totally different machine postures.

These latest evolutions of the net platform made it each more difficult and extra attention-grabbing to design merchandise. They’re nice alternatives for us to interrupt out of our rectangular bins.
I’d like to speak a few new function just like the above: the Window Controls Overlay for Progressive Net Apps (PWAs).
Progressive Net Apps are blurring the traces between apps and web sites. They mix the very best of each worlds. On one hand, they’re secure, linkable, searchable, and responsive similar to web sites. However, they supply further highly effective capabilities, work offline, and skim recordsdata similar to native apps.
As a design floor, PWAs are actually attention-grabbing as a result of they problem us to consider what mixing internet and device-native consumer interfaces will be. On desktop gadgets specifically, now we have greater than 40 years of historical past telling us what functions ought to seem like, and it may be arduous to interrupt out of this psychological mannequin.
On the finish of the day although, PWAs on desktop are constrained to the window they seem in: a rectangle with a title bar on the prime.
Right here’s what a typical desktop PWA app seems to be like:

Positive, because the writer of a PWA, you get to decide on the colour of the title bar (utilizing the Net Software Manifest theme_color property), however that’s about it.
What if we might assume outdoors this field, and reclaim the true property of the app’s whole window? Doing so would give us an opportunity to make our apps extra lovely and really feel extra built-in within the working system.
That is precisely what the Window Controls Overlay provides. This new PWA performance makes it potential to reap the benefits of the complete floor space of the app, together with the place the title bar usually seems.
Concerning the title bar and window controls#section2
Let’s begin with a proof of what the title bar and window controls are.
The title bar is the world displayed on the prime of an app window, which normally comprises the app’s identify. Window controls are the affordances, or buttons, that make it potential to reduce, maximize, or shut the app’s window, and are additionally displayed on the prime.
Window Controls Overlay removes the bodily constraint of the title bar and window controls areas. It frees up the complete peak of the app window, enabling the title bar and window management buttons to be overlaid on prime of the appliance’s internet content material.
In case you are studying this text on a desktop laptop, take a fast take a look at different apps. Chances are high they’re already doing one thing just like this. Actually, the very internet browser you might be utilizing to learn this makes use of the highest space to show tabs.
Spotify shows album paintings all the way in which to the highest fringe of the appliance window.
Microsoft Phrase makes use of the out there title bar area to show the auto-save and search functionalities, and extra.
The entire level of this function is to let you make use of this area with your personal content material whereas offering a method to account for the window management buttons. And it allows you to supply this modified expertise on a variety of platforms whereas not adversely affecting the expertise on browsers or gadgets that don’t help Window Controls Overlay. In any case, PWAs are all about progressive enhancement, so this function is an opportunity to reinforce your app to make use of this additional area when it’s out there.
Let’s use the function#section3
For the remainder of this text, we’ll be engaged on a demo app to be taught extra about utilizing the function.
The demo app known as 1DIV. It’s a easy CSS playground the place customers can create designs utilizing CSS and a single HTML aspect.
The app has two pages. The primary lists the prevailing CSS designs you’ve created:
The second web page allows you to create and edit CSS designs:
Since I’ve added a easy internet manifest and repair employee, we are able to set up the app as a PWA on desktop. Here’s what it seems to be like on macOS:

And on Home windows:

Our app is trying good, however the white title bar within the first web page is wasted area. Within the second web page, it might be very nice if the design space went all the way in which to the highest of the app window.
Let’s use the Window Controls Overlay function to enhance this.
Enabling Window Controls Overlay#section4
The function continues to be experimental in the mean time. To strive it, it’s worthwhile to allow it in one of many supported browsers.
As of now, it has been carried out in Chromium, as a collaboration between Microsoft and Google. We are able to subsequently use it in Chrome or Edge by going to the inner about://flags web page, and enabling the Desktop PWA Window Controls Overlay flag.
Utilizing Window Controls Overlay#section5
To make use of the function, we have to add the next display_override member to our internet app’s manifest file:
{
"identify": "1DIV",
"description": "1DIV is a mini CSS playground",
"lang": "en-US",
"start_url": "/",
"theme_color": "#ffffff",
"background_color": "#ffffff",
"display_override": [
"window-controls-overlay"
],
"icons": [
...
]
}
On the floor, the function is de facto easy to make use of. This manifest change is the one factor we have to make the title bar disappear and switch the window controls into an overlay.
Nonetheless, to offer a terrific expertise for all customers no matter what machine or browser they use, and to profit from the title bar space in our design, we’ll want a little bit of CSS and JavaScript code.
Here’s what the app seems to be like now:
The title bar is gone, which is what we wished, however our brand, search subject, and NEW button are partially coated by the window controls as a result of now our format begins on the prime of the window.
It’s related on Home windows, with the distinction that the shut, maximize, and reduce buttons seem on the appropriate facet, grouped along with the PWA management buttons:
Utilizing CSS to maintain away from the window controls#section6
Together with the function, new CSS setting variables have been launched:
titlebar-area-x
titlebar-area-y
titlebar-area-width
titlebar-area-height
You utilize these variables with the CSS env() operate to place your content material the place the title bar would have been whereas making certain it gained’t overlap with the window controls. In our case, we’ll use two of the variables to place our header, which comprises the emblem, search bar, and NEW button.
header {
place: absolute;
left: env(titlebar-area-x, 0);
width: env(titlebar-area-width, 100%);
peak: var(--toolbar-height);
}
The titlebar-area-x
variable provides us the space from the left of the viewport to the place the title bar would seem, and titlebar-area-width
is its width. (Bear in mind, this isn’t equal to the width of the whole viewport, simply the title bar portion, which as famous earlier, doesn’t embody the window controls.)
By doing this, we ensure our content material stays totally seen. We’re additionally defining fallback values (the second parameter within the env()
operate) for when the variables are usually not outlined (resembling on non-supporting browsers, or when the Home windows Management Overlay function is disabled).
Now our header adapts to its environment, and it doesn’t really feel just like the window management buttons have been added as an afterthought. The app seems to be much more like a local app.
Altering the window controls background shade so it blends in#section7
Now let’s take a better take a look at our second web page: the CSS playground editor.

Not nice. Our CSS demo space does go all the way in which to the highest, which is what we wished, however the way in which the window controls seem as white rectangles on prime of it’s fairly jarring.
We are able to repair this by altering the app’s theme shade. There are a few methods to outline it:
- PWAs can outline a theme shade within the internet app manifest file utilizing the theme_color manifest member. This shade is then utilized by the OS in numerous methods. On desktop platforms, it’s used to offer a background shade to the title bar and window controls.
- Web sites can use the theme-color meta tag as properly. It’s utilized by browsers to customise the colour of the UI across the internet web page. For PWAs, this shade can override the manifest
theme_color
.
In our case, we are able to set the manifest theme_color
to white to offer the appropriate default shade for our app. The OS will learn this shade worth when the app is put in and use it to make the window controls background shade white. This shade works nice for our most important web page with the checklist of demos.
The theme-color
meta tag will be modified at runtime, utilizing JavaScript. So we are able to try this to override the white with the appropriate demo background shade when one is opened.
Right here is the operate we’ll use:
operate themeWindow(bgColor) {
doc.querySelector("meta[name=theme-color]").setAttribute('content material', bgColor);
}
With this in place, we are able to think about how utilizing shade and CSS transitions can produce a clean change from the checklist web page to the demo web page, and allow the window management buttons to mix in with the remainder of the app’s interface.
Dragging the window#section8
Now, eliminating the title bar totally does have an necessary accessibility consequence: it’s way more tough to maneuver the appliance window round.
The title bar offers a large space for customers to click on and drag, however by utilizing the Window Controls Overlay function, this space turns into restricted to the place the management buttons are, and customers need to very exactly purpose between these buttons to maneuver the window.
Fortuitously, this may be mounted utilizing CSS with the app-region
property. This property is, for now, solely supported in Chromium-based browsers and desires the -webkit-
vendor prefix.
To make any aspect of the app turn into a dragging goal for the window, we are able to use the next:
-webkit-app-region: drag;
Additionally it is potential to explicitly make a component non-draggable:
-webkit-app-region: no-drag;
These choices will be helpful for us. We are able to make the whole header a dragging goal, however make the search subject and NEW button inside it non-draggable to allow them to nonetheless be used as regular.
Nonetheless, as a result of the editor web page doesn’t show the header, customers wouldn’t have the ability to drag the window whereas modifying code. So let’s use a special method. We’ll create one other aspect earlier than our header, additionally completely positioned, and devoted to dragging the window.
<div class="drag"></div>
<header>...</header>
.drag {
place: absolute;
prime: 0;
width: 100%;
peak: env(titlebar-area-height, 0);
-webkit-app-region: drag;
}
With the above code, we’re making the draggable space span the whole viewport width, and utilizing the titlebar-area-height
variable to make it as tall as what the title bar would have been. This manner, our draggable space is aligned with the window management buttons as proven beneath.
And, now, to ensure our search subject and button stay usable:
header .search,
header .new {
-webkit-app-region: no-drag;
}
With the above code, customers can click on and drag the place the title bar was. It’s an space that customers anticipate to have the ability to use to maneuver home windows on desktop, and we’re not breaking this expectation, which is nice.
Adapting to window resize#section9
It might be helpful for an app to know each whether or not the window controls overlay is seen and when its measurement modifications. In our case, if the consumer made the window very slim, there wouldn’t be sufficient area for the search subject, brand, and button to suit, so we’d need to push them down a bit.
The Window Controls Overlay function comes with a JavaScript API we are able to use to do that: navigator.windowControlsOverlay
.
The API offers three attention-grabbing issues:
navigator.windowControlsOverlay.seen
lets us know whether or not the overlay is seen.navigator.windowControlsOverlay.getBoundingClientRect()
lets us know the place and measurement of the title bar space.navigator.windowControlsOverlay.ongeometrychange
lets us know when the dimensions or visibility modifications.
Let’s use this to pay attention to the dimensions of the title bar space and transfer the header down if it’s too slim.
if (navigator.windowControlsOverlay) {
navigator.windowControlsOverlay.addEventListener('geometrychange', () => {
const { width } = navigator.windowControlsOverlay.getBoundingClientRect();
doc.physique.classList.toggle('slim', width < 250);
});
}
Within the instance above, we set the slim
class on the physique
of the app if the title bar space is narrower than 250px. We might do one thing related with a media question, however utilizing the windowControlsOverlay
API has two benefits for our use case:
- It’s solely fired when the function is supported and used; we don’t need to adapt the design in any other case.
- We get the dimensions of the title bar space throughout working programs, which is nice as a result of the dimensions of the window controls is totally different on Mac and Home windows. Utilizing a media question wouldn’t make it potential for us to know precisely how a lot area stays.
.slim header {
prime: env(titlebar-area-height, 0);
left: 0;
width: 100%;
}
Utilizing the above CSS code, we are able to transfer our header down to remain away from the window management buttons when the window is simply too slim, and transfer the thumbnails down accordingly.
Thirty pixels of thrilling design alternatives#section10
Utilizing the Window Controls Overlay function, we had been in a position to take our easy demo app and switch it into one thing that feels a lot extra built-in on desktop gadgets. One thing that reaches out of the same old window constraints and offers a customized expertise for its customers.
In actuality, this function solely provides us about 30 pixels of additional room and comes with challenges on tips on how to cope with the window controls. And but, this additional room and people challenges will be become thrilling design alternatives.
Extra gadgets of all shapes and types get invented on a regular basis, and the net retains on evolving to adapt to them. New options get added to the net platform to permit us, internet authors, to combine increasingly deeply with these gadgets. From watches or foldable gadgets to desktop computer systems, we have to evolve our design method for the net. Constructing for the net now lets us assume outdoors the oblong field.
So let’s embrace this. Let’s use the usual applied sciences already at our disposal, and experiment with new concepts to offer tailor-made experiences for all gadgets, all from a single codebase!
In case you get an opportunity to strive the Window Controls Overlay function and have suggestions about it, you’ll be able to open points on the spec’s repository. It’s nonetheless early within the improvement of this function, and you may assist make it even higher. Or, you’ll be able to check out the function’s current documentation, or this demo app and its supply code.