with the built-in UI for OH3 there is the overview page which I completely designed for an ipad which includes multiple columns.
This overview page doesn’t look nice on an iPhone as there are too many columns.
Is it possible like you can do with Habpanel that you can have a different UI per device ?
I know I can create separate pages that fit on the iphone but the side menus cannot be seperated and I can not,have multiple overview pages.
You need a responsive layout using flex
see this post, point number 2.
edit: the below solution by @ysc is much better. 
With the blocks, rows and columns layout, you have to configure your column options, either with these buttons:
or the YAML, for example like this:
config:
label: Overview
blocks:
- component: oh-block
config: {}
slots:
default:
- component: oh-grid-row
config: {}
slots:
default:
- component: oh-grid-col
config:
width: "100"
small: "50"
medium: "33"
slots:
default: []
- component: oh-grid-col
config:
width: "100"
small: "50"
medium: "33"
slots:
default: []
- component: oh-grid-col
config:
width: "100"
medium: "33"
slots:
default: []
The width is the default, so if you plan for phones (and you should) that would be the maximum size allowed for your column (often 100%), and then you select how much you want them to decrease when the screens get larger.
That’s how you end up with a responsive design:
Wow, thank you so much, it’s working perfect now 
