Move backgroundColor to a separate file and introduce dedicated test

web/core/src/jsMain/kotlin/androidx/compose/web/css/CSSProperties.kt

@@ -33,14 +33,6 @@ fun StyleBuilder.color(value: CSSColorValue) {
     property("color", value)
 }
 
-fun StyleBuilder.backgroundColor(value: CSSColorValue) {
-    property("background-color", value)
-}
-
-fun StyleBuilder.backgroundColor(value: String) {
-    property("background-color", value)
-}
-
 @Suppress("EqualsOrHashCode")
 class CSSBorder : CSSStyleValue {
     var width: CSSNumeric? = null

web/core/src/jsMain/kotlin/androidx/compose/web/css/properties/background.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2020-2021 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE.txt file.
+ */
+
+package org.jetbrains.compose.web.css
+
+fun StyleBuilder.backgroundColor(value: String) {
+    property("background-color", value)
+}
+
+fun StyleBuilder.backgroundColor(value: CSSColorValue) {
+    property("background-color", value)
+}
+
+fun StyleBuilder.backgroundColor(value: String) {
+    property("background-color", value)
+}

web/core/src/jsTest/kotlin/css/CSSBackgroundTests.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2020-2021 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE.txt file.
+ */
+
+package org.jetbrains.compose.web.core.tests.css
+
+import kotlinx.browser.window
+import org.jetbrains.compose.web.core.tests.runTest
+import org.jetbrains.compose.web.css.backgroundColor
+import org.jetbrains.compose.web.dom.Div
+import org.w3c.dom.HTMLElement
+import org.w3c.dom.get
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class CSSBackgroundTests {
+    @Test
+    fun backgroundColor() = runTest {
+        composition {
+            Div({style {
+                backgroundColor("rgb(0, 128, 0)")
+            }})
+            Div({style {
+                backgroundColor("rgba(0, 129, 0, 0.2)")
+            }})
+        }
+
+        assertEquals("rgb(0, 128, 0)", window.getComputedStyle(root.children[0] as HTMLElement).backgroundColor)
+        assertEquals("rgba(0, 129, 0, 0.2)", window.getComputedStyle(root.children[1] as HTMLElement).backgroundColor)
+    }
+}