A modern programming language that makes developers happier.

kotlinlang

Why is `Surface` as a root composable in every example? Isn’t it supposed to be some sort of `Background` (which doesnt exist in material theme)?

(also, why not expose the `BoxScope` in the content lambda? Now I need to add another needless `Box`  if I need alignment)

```setContent {
    MyTheme {
        Surface(
        	modifier = Modifier.fillMaxSize(),
        	color = MaterialTheme.color.background
        ) {
        	...
        }
    }
}```

`Surface` is used a lot, because it correctly updates composition local colors to use the correct `on` colors such as `onPrimary` and `onError`.

right, but the defaults are wrong then, default color is surfaceVariant, not `background`

I still need to apply it myself somewhere right?

With that example the everything inside the surface will default to using `onBackground` color until you change it or create another Surface.

I know, just in terms of the library, I think there is some sort of `Background` composable missing

which would then automatically pickup the `MaterialTheme.colorScheme.background` etc.

Seems like the different scaffolds should do something with it.

okay now I see it there

```@Composable
fun Scaffold(
...    backgroundColor: Color = MaterialTheme.colors.background,```

anyways, say I need a Box at the top level, to align some child to the edge, is it not wasteful to add a Box inside the Surface, when Surface is the box, but the `content` lambda is not `BoxScope` :confused:

<@U01D56B2A2H> follow up question please, what if every “screen” has the same background color

Then I’d have a need to set the color just via the xml theme (windowBackground) as to reduce overdraw

It would look the same, however then the `on` colors wouldn’t be setup correctly as you said

any way around that?

&gt; why not expose the `BoxScope` in the content lambda
I guess the reason is that Box is just an implementation detail and `Surface` is not really a layout, just a convenience wrapper for your UI that gives you some properties. Some of them are the CompositionLocal values setup.

&gt; the `on` colors wouldn’t be setup correctly as you said. Any way around that?
You can set them up yourself the same way Surface does.
```CompositionLocalProvider(
    LocalContentColor provides contentColor
) { ... }```
