Warning, /frameworks/kirigami/examples/sizegroup.qml is written in an unsupported language. File is not indexed.

 import QtQuick 2.15
 import QtQuick.Layouts 1.15
 import QtQuick.Controls 2.15 as Controls
 import org.kde.kirigami 2.20 as Kirigami
 
 Kirigami.ApplicationWindow {
     pageStack.initialPage: Kirigami.Page {
         Kirigami.SizeGroup {
             items: [rect1, rect2, rect3]
             mode: Kirigami.SizeGroup.Width
         }
         RowLayout {
             id: layout
             anchors.fill: parent
 
             Rectangle {
                 id: rect1
                 color: "red"
                 height: 100
                 width: 400
             }
             Rectangle {
                 id: rect2
                 color: "green"
                 height: 100
                 implicitWidth: 150
             }
             Rectangle {
                 id: rect3
                 color: "blue"
                 height: 100
                 implicitWidth: 200
             }
         }
     }
 }