CSS is about styling packing containers. The truth is, the entire internet is manufactured from packing containers, from the browser viewport to parts on a web page. However each every now and then a brand new function comes alongside that makes us rethink our design strategy.
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Spherical shows, for instance, make it enjoyable to play with round clip areas. Cell display screen notches and digital keyboards provide challenges to finest set up content material that stays away from them. And twin display screen or foldable gadgets make us rethink tips on how to finest use obtainable house in plenty of completely different machine postures.

These current evolutions of the online platform made it each tougher and extra fascinating to design merchandise. They’re nice alternatives for us to interrupt out of our rectangular packing containers.
I’d like to speak a couple of new function much 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 most effective of each worlds. On one hand, they’re secure, linkable, searchable, and responsive identical to web sites. Alternatively, they supply further highly effective capabilities, work offline, and skim recordsdata identical to native apps.
As a design floor, PWAs are actually fascinating as a result of they problem us to consider what mixing internet and device-native person interfaces might be. On desktop gadgets specifically, we now have greater than 40 years of historical past telling us what purposes ought to appear to be, and it may be onerous 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 appears to be like like:

Certain, because the writer of a PWA, you get to decide on the colour of the title bar (utilizing the Net Utility 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 stunning and really feel extra built-in within the working system.
That is precisely what the Window Controls Overlay gives. This new PWA performance makes it doable to benefit from the total 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 incorporates the app’s title. Window controls are the affordances, or buttons, that make it doable 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 total 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.
If you’re studying this text on a desktop pc, take a fast take a look at different apps. Chances are high they’re already doing one thing much like this. The truth is, the very internet browser you might be utilizing to learn this makes use of the highest space to show tabs.
Spotify shows album art work all the best way to the highest fringe of the appliance window.
Microsoft Phrase makes use of the obtainable title bar house to show the auto-save and search functionalities, and extra.
The entire level of this function is to help you make use of this house with your individual content material whereas offering a approach to account for the window management buttons. And it allows you to provide this modified expertise on a spread of platforms whereas not adversely affecting the expertise on browsers or gadgets that don’t assist Window Controls Overlay. In any case, PWAs are all about progressive enhancement, so this function is an opportunity to boost your app to make use of this additional house when it’s obtainable.
Let’s use the function#section3
For the remainder of this text, we’ll be engaged on a demo app to study 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 present 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 will set up the app as a PWA on desktop. Here’s what it appears to be like like on macOS:

And on Home windows:

Our app is trying good, however the white title bar within the first web page is wasted house. Within the second web page, it might be very nice if the design space went all the best way 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 remains to be experimental for the time being. To attempt it, you want 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 due to this fact 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:
{
"title": "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 absolutely 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.
Nevertheless, to offer an important expertise for all customers no matter what machine or browser they use, and to take advantage of the title bar space in our design, we’ll want a little bit of CSS and JavaScript code.
Here’s what the app appears to be like like now:
The title bar is gone, which is what we wished, however our brand, search discipline, and NEW button are partially coated by the window controls as a result of now our structure begins on the prime of the window.
It’s comparable on Home windows, with the distinction that the shut, maximize, and reduce buttons seem on the fitting facet, grouped along with the PWA management buttons:
Utilizing CSS to maintain away from the window controls#section6
Together with the function, new CSS atmosphere variables have been launched:
titlebar-area-x
titlebar-area-y
titlebar-area-width
titlebar-area-height
You employ these variables with the CSS env() operate to place your content material the place the title bar would have been whereas making certain it received’t overlap with the window controls. In our case, we’ll use two of the variables to place our header, which incorporates the brand, 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 offers us the space from the left of the viewport to the place the title bar would seem, and titlebar-area-width
is its width. (Keep in mind, this isn’t equal to the width of your entire viewport, simply the title bar portion, which as famous earlier, doesn’t embrace the window controls.)
By doing this, we ensure that our content material stays absolutely seen. We’re additionally defining fallback values (the second parameter within the env()
operate) for when the variables are usually not outlined (akin to 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 appears to be like much more like a local app.
Altering the window controls background shade so it blends in#section7
Now let’s take a more in-depth take a look at our second web page: the CSS playground editor.

Not nice. Our CSS demo space does go all the best way to the highest, which is what we wished, however the best way 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 several 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 nicely. 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 will set the manifest theme_color
to white to offer the fitting 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 important web page with the listing of demos.
The theme-color
meta tag might be modified at runtime, utilizing JavaScript. So we will try this to override the white with the fitting 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 will think about how utilizing shade and CSS transitions can produce a clean change from the listing 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 solely does have an vital accessibility consequence: it’s rather more tough to maneuver the appliance window round.
The title bar supplies 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 should very exactly goal 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 grow to be a dragging goal for the window, we will use the next:
-webkit-app-region: drag;
Additionally it is doable to explicitly make a component non-draggable:
-webkit-app-region: no-drag;
These choices might be helpful for us. We are able to make your entire header a dragging goal, however make the search discipline and NEW button inside it non-draggable to allow them to nonetheless be used as regular.
Nevertheless, as a result of the editor web page doesn’t show the header, customers wouldn’t be capable of drag the window whereas enhancing code. So let’s use a unique strategy. 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 your entire 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 under.
And, now, to verify our search discipline 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 count on to have the ability to use to maneuver home windows on desktop, and we’re not breaking this expectation, which is sweet.
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 dimension adjustments. In our case, if the person made the window very slim, there wouldn’t be sufficient house for the search discipline, 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 will use to do that: navigator.windowControlsOverlay
.
The API supplies three fascinating issues:
navigator.windowControlsOverlay.seen
lets us know whether or not the overlay is seen.navigator.windowControlsOverlay.getBoundingClientRect()
lets us know the place and dimension of the title bar space.navigator.windowControlsOverlay.ongeometrychange
lets us know when the dimensions or visibility adjustments.
Let’s use this to concentrate on 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 comparable 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 methods, which is nice as a result of the dimensions of the window controls is completely different on Mac and Home windows. Utilizing a media question wouldn’t make it doable for us to know precisely how a lot house stays.
.slim header {
prime: env(titlebar-area-height, 0);
left: 0;
width: 100%;
}
Utilizing the above CSS code, we will transfer our header down to remain away from the window management buttons when the window is just too slim, and transfer the thumbnails down accordingly.
Thirty pixels of thrilling design alternatives#section10
Utilizing the Window Controls Overlay function, we had been capable of 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 standard window constraints and supplies a customized expertise for its customers.
In actuality, this function solely offers us about 30 pixels of additional room and comes with challenges on tips on how to take care of the window controls. And but, this additional room and people challenges might be changed into thrilling design alternatives.
Extra gadgets of all shapes and types get invented on a regular basis, and the online retains on evolving to adapt to them. New options get added to the online 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 strategy for the online. Constructing for the online 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!
If you happen to get an opportunity to attempt the Window Controls Overlay function and have suggestions about it, you may 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 may check out the function’s current documentation, or this demo app and its supply code.