Updates the intelliJPlugin example with currently IDEA Theme colors (#351)

examples/intelliJPlugin/src/main/kotlin/com/jetbrains/compose/theme/Theme.kt

@@ -5,17 +5,14 @@ import androidx.compose.material.darkColors
 import androidx.compose.material.lightColors
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.graphics.Color
+import com.jetbrains.compose.theme.intellij.SwingColor
 
 private val DarkGreenColorPalette = darkColors(
     primary = green200,
     primaryVariant = green700,
     secondary = teal200,
-    background = Color.Black,
-    surface = Color(74, 74, 74),
     onPrimary = Color.Black,
     onSecondary = Color.White,
-    onBackground = Color.White,
-    onSurface = Color.White,
     error = Color.Red,
 )
 
@@ -23,11 +20,7 @@ private val LightGreenColorPalette = lightColors(
     primary = green500,
     primaryVariant = green700,
     secondary = teal200,
-    background = Color.White,
-    surface = Color.White,
     onPrimary = Color.White,
-    onSecondary = Color.Black,
-    onBackground = Color.Black,
     onSurface = Color.Black
 )
 
@@ -37,9 +30,15 @@ fun WidgetTheme(
     content: @Composable() () -> Unit,
 ) {
     val colors = if (darkTheme) DarkGreenColorPalette else LightGreenColorPalette
+    val swingColor = SwingColor()
 
     MaterialTheme(
-        colors = colors,
+        colors = colors.copy(
+            background = swingColor.background,
+            onBackground = swingColor.onBackground,
+            surface = swingColor.background,
+            onSurface = swingColor.onBackground,
+        ),
         typography = typography,
         shapes = shapes,
         content = content

examples/intelliJPlugin/src/main/kotlin/com/jetbrains/compose/theme/intellij/SwingColor.kt

@@ -0,0 +1,61 @@
+package com.jetbrains.compose.theme.intellij
+
+import androidx.compose.runtime.*
+import androidx.compose.ui.graphics.Color
+import com.intellij.ide.ui.LafManagerListener
+import com.intellij.openapi.application.ApplicationManager
+import javax.swing.UIManager
+import java.awt.Color as AWTColor
+
+interface SwingColor {
+    val background: Color
+    val onBackground: Color
+}
+
+@Composable
+fun SwingColor(): SwingColor {
+    val swingColor = remember { SwingColorImpl() }
+
+    val messageBus = remember {
+        ApplicationManager.getApplication().messageBus.connect()
+    }
+
+    remember(messageBus) {
+        messageBus.subscribe(
+            LafManagerListener.TOPIC,
+            ThemeChangeListener(swingColor::updateCurrentColors)
+        )
+    }
+
+    DisposableEffect(messageBus) {
+        onDispose {
+            messageBus.disconnect()
+        }
+    }
+
+    return swingColor
+}
+
+private class SwingColorImpl : SwingColor {
+    private val _backgroundState: MutableState<Color> = mutableStateOf(getBackgroundColor)
+    private val _onBackgroundState: MutableState<Color> = mutableStateOf(getOnBackgroundColor)
+
+    override val background: Color get() = _backgroundState.value
+    override val onBackground: Color get() = _onBackgroundState.value
+
+    private val getBackgroundColor get() = getColor(BACKGROUND_KEY)
+    private val getOnBackgroundColor get() = getColor(ON_BACKGROUND_KEY)
+
+    fun updateCurrentColors() {
+        _backgroundState.value = getBackgroundColor
+        _onBackgroundState.value = getOnBackgroundColor
+    }
+
+    private val AWTColor.asComposeColor: Color get() = Color(red, green, blue, alpha)
+    private fun getColor(key: String): Color = UIManager.getColor(key).asComposeColor
+
+    companion object {
+        private const val BACKGROUND_KEY = "Panel.background"
+        private const val ON_BACKGROUND_KEY = "Panel.foreground"
+    }
+}

examples/intelliJPlugin/src/main/kotlin/com/jetbrains/compose/theme/intellij/ThemeChangeListener.kt

@@ -0,0 +1,13 @@
+package com.jetbrains.compose.theme.intellij
+
+import com.intellij.ide.ui.LafManager
+import com.intellij.ide.ui.LafManagerListener
+
+internal class ThemeChangeListener(
+    val updateColors: () -> Unit
+) : LafManagerListener {
+    override fun lookAndFeelChanged(source: LafManager) {
+        updateColors()
+    }
+}
+