fix: toggle map color scheme from system state

maps-app/src/main/java/com/google/maps/android/compose/BasicMapActivity.kt

@@ -25,6 +25,7 @@ import androidx.compose.animation.fadeOut
 import androidx.compose.foundation.ScrollState
 import androidx.compose.foundation.background
 import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -167,6 +168,7 @@ fun GoogleMapView(
     var mapVisible by remember { mutableStateOf(true) }
 
     var darkMode by remember { mutableStateOf(mapColorScheme) }
+    val systemInDarkTheme = isSystemInDarkTheme()
 
     if (mapVisible) {
         GoogleMap(
@@ -303,11 +305,7 @@ fun GoogleMapView(
             MapButton(
                 text = "Toggle Dark Mode",
                 onClick = {
-                    darkMode =
-                        if (darkMode == ComposeMapColorScheme.DARK)
-                            ComposeMapColorScheme.LIGHT
-                        else
-                            ComposeMapColorScheme.DARK
+                    darkMode = toggledMapColorScheme(darkMode, systemInDarkTheme)
                 },
                 modifier = Modifier
                     .testTag("toggleDarkMode")
@@ -347,6 +345,19 @@ fun GoogleMapView(
     }
 }
 
+internal fun toggledMapColorScheme(
+    current: ComposeMapColorScheme,
+    systemInDarkTheme: Boolean,
+): ComposeMapColorScheme = when (current) {
+    ComposeMapColorScheme.LIGHT -> ComposeMapColorScheme.DARK
+    ComposeMapColorScheme.DARK -> ComposeMapColorScheme.LIGHT
+    ComposeMapColorScheme.FOLLOW_SYSTEM -> if (systemInDarkTheme) {
+        ComposeMapColorScheme.LIGHT
+    } else {
+        ComposeMapColorScheme.DARK
+    }
+}
+
 @Composable
 private fun MapTypeControls(
     onMapTypeClick: (MapType) -> Unit

maps-app/src/test/java/com/google/maps/android/compose/BasicMapActivityTest.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.maps.android.compose
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+
+class BasicMapActivityTest {
+
+    @Test
+    fun lightSchemeTogglesToDark() {
+        val result = toggledMapColorScheme(
+            current = ComposeMapColorScheme.LIGHT,
+            systemInDarkTheme = false,
+        )
+
+        assertThat(result).isEqualTo(ComposeMapColorScheme.DARK)
+    }
+
+    @Test
+    fun darkSchemeTogglesToLight() {
+        val result = toggledMapColorScheme(
+            current = ComposeMapColorScheme.DARK,
+            systemInDarkTheme = true,
+        )
+
+        assertThat(result).isEqualTo(ComposeMapColorScheme.LIGHT)
+    }
+
+    @Test
+    fun followSystemTogglesAwayFromEffectiveScheme() {
+        assertThat(
+            toggledMapColorScheme(
+                current = ComposeMapColorScheme.FOLLOW_SYSTEM,
+                systemInDarkTheme = false,
+            )
+        ).isEqualTo(ComposeMapColorScheme.DARK)
+        assertThat(
+            toggledMapColorScheme(
+                current = ComposeMapColorScheme.FOLLOW_SYSTEM,
+                systemInDarkTheme = true,
+            )
+        ).isEqualTo(ComposeMapColorScheme.LIGHT)
+    }
+}