diff --git a/apps/designer/app/canvas/features/wrapper-component/selected-instance-connector.ts b/apps/designer/app/canvas/features/wrapper-component/selected-instance-connector.ts
index 91618761fc..ffe134ef31 100644
--- a/apps/designer/app/canvas/features/wrapper-component/selected-instance-connector.ts
+++ b/apps/designer/app/canvas/features/wrapper-component/selected-instance-connector.ts
@@ -1,6 +1,6 @@
 import { useEffect } from "react";
 import { useStore } from "@nanostores/react";
-import type { Instance, Prop, Styles } from "@webstudio-is/project-build";
+import type { Instance, Prop, StyleDecl } from "@webstudio-is/project-build";
 import { getBrowserStyle } from "@webstudio-is/react-sdk";
 import { publish, subscribe } from "~/shared/pubsub";
 import {
@@ -57,7 +57,7 @@ export const SelectedInstanceConnector = ({
 }: {
   instanceElementRef: { current: undefined | HTMLElement };
   instance: Instance;
-  instanceStyles: Styles;
+  instanceStyles: StyleDecl[];
   instanceProps: undefined | Prop[];
 }) => {
   const rootInstance = useStore(rootInstanceContainer);
diff --git a/apps/designer/app/canvas/shared/styles.ts b/apps/designer/app/canvas/shared/styles.ts
index 60353e7b10..5f3e790a46 100644
--- a/apps/designer/app/canvas/shared/styles.ts
+++ b/apps/designer/app/canvas/shared/styles.ts
@@ -7,7 +7,7 @@ import {
   selectedInstanceIdStore,
   useBreakpoints,
 } from "~/shared/nano-states";
-import type { Styles } from "@webstudio-is/project-build";
+import type { StyleDecl } from "@webstudio-is/project-build";
 import {
   getComponentMeta,
   getComponentNames,
@@ -159,7 +159,7 @@ export const useCssRules = ({
   instanceStyles,
 }: {
   instanceId: string;
-  instanceStyles: Styles;
+  instanceStyles: StyleDecl[];
 }) => {
   const [breakpoints] = useBreakpoints();
 
diff --git a/apps/designer/app/designer/features/breakpoints/breakpoints.tsx b/apps/designer/app/designer/features/breakpoints/breakpoints.tsx
index 3609594df4..8634e512c4 100644
--- a/apps/designer/app/designer/features/breakpoints/breakpoints.tsx
+++ b/apps/designer/app/designer/features/breakpoints/breakpoints.tsx
@@ -69,11 +69,13 @@ export const Breakpoints = () => {
     const [updatedBreakpoints] = store.createTransaction(
       [breakpointsContainer, stylesStore],
       (breakpoints, styles) => {
-        removeByMutable(breakpoints, ({ id }) => id === breakpointToDelete.id);
-        removeByMutable(
-          styles,
-          (style) => style.breakpointId === breakpointToDelete.id
-        );
+        const breakpointId = breakpointToDelete.id;
+        removeByMutable(breakpoints, ({ id }) => id === breakpointId);
+        for (const [styleDeclKey, styleDecl] of styles) {
+          if (styleDecl.breakpointId === breakpointId) {
+            styles.delete(styleDeclKey);
+          }
+        }
       }
     );
     if (breakpointToDelete === selectedBreakpoint) {
diff --git a/apps/designer/app/designer/features/style-panel/shared/style-info.test.ts b/apps/designer/app/designer/features/style-panel/shared/style-info.test.ts
index e6e492e6ed..720dc3409f 100644
--- a/apps/designer/app/designer/features/style-panel/shared/style-info.test.ts
+++ b/apps/designer/app/designer/features/style-panel/shared/style-info.test.ts
@@ -1,5 +1,5 @@
 import type { Breakpoint } from "@webstudio-is/css-data";
-import type { Instance, Styles } from "@webstudio-is/project-build";
+import type { Instance, StyleDecl } from "@webstudio-is/project-build";
 import {
   getCascadedBreakpointIds,
   getCascadedInfo,
@@ -36,7 +36,7 @@ const cascadedBreakpointIds = getCascadedBreakpointIds(
   selectedBreakpointId
 );
 
-const cascadingStylesByInstanceId = new Map<Instance["id"], Styles>();
+const cascadingStylesByInstanceId = new Map<Instance["id"], StyleDecl[]>();
 cascadingStylesByInstanceId.set(selectedInstanceId, [
   {
     breakpointId: "1",
@@ -92,7 +92,7 @@ const rootInstance: Instance = {
   ],
 };
 
-const inheritingStylesByInstanceId = new Map<Instance["id"], Styles>();
+const inheritingStylesByInstanceId = new Map<Instance["id"], StyleDecl[]>();
 inheritingStylesByInstanceId.set("1", [
   // should be inherited even from another breakpoint
   {
diff --git a/apps/designer/app/designer/features/style-panel/shared/style-info.ts b/apps/designer/app/designer/features/style-panel/shared/style-info.ts
index 6ac5fc75bf..2973d0fe69 100644
--- a/apps/designer/app/designer/features/style-panel/shared/style-info.ts
+++ b/apps/designer/app/designer/features/style-panel/shared/style-info.ts
@@ -10,7 +10,7 @@ import { properties } from "@webstudio-is/css-data";
 import { utils } from "@webstudio-is/project";
 import type {
   Instance,
-  Styles,
+  StyleDecl,
   StyleSource as StyleSourceType,
 } from "@webstudio-is/project-build";
 import {
@@ -81,7 +81,7 @@ for (const [property, value] of Object.entries(properties)) {
 }
 
 const getSelectedStyle = (
-  stylesByStyleSourceId: Map<StyleSourceType["id"], Styles>,
+  stylesByStyleSourceId: Map<StyleSourceType["id"], StyleDecl[]>,
   breakpointId: string,
   styleSourceId: string
 ) => {
@@ -121,7 +121,7 @@ export const getCascadedBreakpointIds = (
  * affecting current view
  */
 export const getCascadedInfo = (
-  stylesByInstanceId: Map<Instance["id"], Styles>,
+  stylesByInstanceId: Map<Instance["id"], StyleDecl[]>,
   instanceId: string,
   cascadedBreakpointIds: string[]
 ) => {
@@ -149,7 +149,7 @@ export const getCascadedInfo = (
  */
 export const getInheritedInfo = (
   rootInstance: Instance,
-  stylesByInstanceId: Map<Instance["id"], Styles>,
+  stylesByInstanceId: Map<Instance["id"], StyleDecl[]>,
   instanceId: string,
   cascadedBreakpointIds: string[],
   selectedBreakpointId: string
diff --git a/apps/designer/app/designer/features/style-panel/shared/use-style-data.ts b/apps/designer/app/designer/features/style-panel/shared/use-style-data.ts
index 6c30c3cdbb..b3562d1d9b 100644
--- a/apps/designer/app/designer/features/style-panel/shared/use-style-data.ts
+++ b/apps/designer/app/designer/features/style-panel/shared/use-style-data.ts
@@ -1,7 +1,7 @@
 import { useCallback } from "react";
 import store from "immerhin";
 import warnOnce from "warn-once";
-import type { Instance } from "@webstudio-is/project-build";
+import { getStyleDeclKey, type Instance } from "@webstudio-is/project-build";
 import type { StyleUpdates } from "@webstudio-is/project";
 import type { StyleProperty, StyleValue } from "@webstudio-is/css-data";
 import { type Publish } from "~/shared/pubsub";
@@ -12,10 +12,6 @@ import {
   stylesStore,
 } from "~/shared/nano-states";
 import { useSelectedBreakpoint } from "~/designer/shared/nano-states";
-import {
-  removeByMutable,
-  replaceByOrAppendMutable,
-} from "~/shared/array-utils";
 // @todo: must be removed, now it's only for compatibility with existing code
 import { parseCssValue } from "./parse-css-value";
 import { useStyleInfo } from "./style-info";
@@ -101,29 +97,22 @@ export const useStyleData = ({ selectedInstance, publish }: UseStyleData) => {
 
           for (const update of updates) {
             if (update.operation === "set") {
-              replaceByOrAppendMutable(
-                styles,
-                {
-                  breakpointId,
-                  styleSourceId,
-                  property: update.property,
-                  value: update.value,
-                },
-                (item) =>
-                  item.styleSourceId === styleSourceId &&
-                  item.breakpointId === breakpointId &&
-                  item.property === update.property
-              );
+              const styleDecl = {
+                breakpointId,
+                styleSourceId,
+                property: update.property,
+                value: update.value,
+              };
+              styles.set(getStyleDeclKey(styleDecl), styleDecl);
             }
 
             if (update.operation === "delete") {
-              removeByMutable(
-                styles,
-                (item) =>
-                  item.styleSourceId === styleSourceId &&
-                  item.breakpointId === breakpointId &&
-                  item.property === update.property
-              );
+              const styleDeclKey = getStyleDeclKey({
+                breakpointId,
+                styleSourceId,
+                property: update.property,
+              });
+              styles.delete(styleDeclKey);
             }
           }
         }
diff --git a/apps/designer/app/shared/copy-paste/copy-paste-instance.ts b/apps/designer/app/shared/copy-paste/copy-paste-instance.ts
index ca4936b0e1..e30fa91f6a 100644
--- a/apps/designer/app/shared/copy-paste/copy-paste-instance.ts
+++ b/apps/designer/app/shared/copy-paste/copy-paste-instance.ts
@@ -2,9 +2,10 @@ import store from "immerhin";
 import { z } from "zod";
 import { useEffect } from "react";
 import {
+  getStyleDeclKey,
   Instance,
   Prop,
-  Styles,
+  StyleDecl,
   StyleSource,
   StyleSourceSelection,
 } from "@webstudio-is/project-build";
@@ -37,7 +38,7 @@ const InstanceData = z.object({
   props: z.array(Prop),
   styleSourceSelections: z.array(StyleSourceSelection),
   styleSources: z.array(StyleSource),
-  styles: Styles,
+  styles: z.array(StyleDecl),
 });
 
 type InstanceData = z.infer<typeof InstanceData>;
@@ -118,7 +119,9 @@ const pasteInstance = (data: InstanceData) => {
       for (const styleSource of data.styleSources) {
         styleSources.set(styleSource.id, styleSource);
       }
-      styles.push(...data.styles);
+      for (const styleDecl of data.styles) {
+        styles.set(getStyleDeclKey(styleDecl), styleDecl);
+      }
     }
   );
   selectedInstanceIdStore.set(data.instance.id);
diff --git a/apps/designer/app/shared/css-utils/generate-css-text.ts b/apps/designer/app/shared/css-utils/generate-css-text.ts
index 3af2ea2f69..bd43430698 100644
--- a/apps/designer/app/shared/css-utils/generate-css-text.ts
+++ b/apps/designer/app/shared/css-utils/generate-css-text.ts
@@ -58,7 +58,7 @@ export const generateCssText = async (
   }
 
   const styleRules = getStyleRules(
-    canvasData.build?.styles,
+    new Map(canvasData.build?.styles),
     new Map(canvasData.tree?.styleSourceSelections)
   );
   for (const { breakpointId, instanceId, style } of styleRules) {
diff --git a/apps/designer/app/shared/instance-utils.ts b/apps/designer/app/shared/instance-utils.ts
index 0bceaab6ed..b4093a302e 100644
--- a/apps/designer/app/shared/instance-utils.ts
+++ b/apps/designer/app/shared/instance-utils.ts
@@ -1,5 +1,5 @@
 import store from "immerhin";
-import { Instance } from "@webstudio-is/project-build";
+import type { Instance } from "@webstudio-is/project-build";
 import {
   rootInstanceContainer,
   propsStore,
@@ -86,9 +86,11 @@ export const deleteInstance = (targetInstanceId: Instance["id"]) => {
       for (const styleSourceId of subtreeLocalStyleSourceIds) {
         styleSources.delete(styleSourceId);
       }
-      removeByMutable(styles, (styleDecl) =>
-        subtreeLocalStyleSourceIds.has(styleDecl.styleSourceId)
-      );
+      for (const [styleDeclKey, styleDecl] of styles) {
+        if (subtreeLocalStyleSourceIds.has(styleDecl.styleSourceId)) {
+          styles.delete(styleDeclKey);
+        }
+      }
 
       selectedInstanceIdStore.set(parentInstance.id);
     }
diff --git a/apps/designer/app/shared/nano-states/nano-states.ts b/apps/designer/app/shared/nano-states/nano-states.ts
index fbac8eb89b..3e3a27fe58 100644
--- a/apps/designer/app/shared/nano-states/nano-states.ts
+++ b/apps/designer/app/shared/nano-states/nano-states.ts
@@ -8,6 +8,8 @@ import {
   Instance,
   Prop,
   Props,
+  StyleDecl,
+  StyleDeclKey,
   Styles,
   StyleSource,
   StyleSources,
@@ -86,11 +88,11 @@ export const useInstanceProps = (instanceId: undefined | Instance["id"]) => {
   return instanceProps;
 };
 
-export const stylesStore = atom<Styles>([]);
+export const stylesStore = atom<Styles>(new Map());
 
-export const useSetStyles = (styles: Styles) => {
+export const useSetStyles = (styles: [StyleDeclKey, StyleDecl][]) => {
   useSyncInitializeOnce(() => {
-    stylesStore.set(styles);
+    stylesStore.set(new Map(styles));
   });
 };
 export const useInstanceStyles = (instanceId: undefined | Instance["id"]) => {
@@ -165,8 +167,8 @@ export const selectedStyleSourceIdStore = atom<undefined | StyleSource["id"]>(
 export const stylesIndexStore = computed(
   [stylesStore, styleSourceSelectionsStore],
   (styles, styleSourceSelections) => {
-    const stylesByStyleSourceId = new Map<StyleSource["id"], Styles>();
-    for (const styleDecl of styles) {
+    const stylesByStyleSourceId = new Map<StyleSource["id"], StyleDecl[]>();
+    for (const styleDecl of styles.values()) {
       const { styleSourceId } = styleDecl;
       let styleSourceStyles = stylesByStyleSourceId.get(styleSourceId);
       if (styleSourceStyles === undefined) {
@@ -176,9 +178,9 @@ export const stylesIndexStore = computed(
       styleSourceStyles.push(styleDecl);
     }
 
-    const stylesByInstanceId = new Map<Instance["id"], Styles>();
+    const stylesByInstanceId = new Map<Instance["id"], StyleDecl[]>();
     for (const { instanceId, values } of styleSourceSelections.values()) {
-      const instanceStyles: Styles = [];
+      const instanceStyles: StyleDecl[] = [];
       for (const styleSourceId of values) {
         const styleSourceStyles = stylesByStyleSourceId.get(styleSourceId);
         if (styleSourceStyles) {
diff --git a/apps/designer/app/shared/tree-utils.test.ts b/apps/designer/app/shared/tree-utils.test.ts
index bf157d1eb9..bd1e0c4385 100644
--- a/apps/designer/app/shared/tree-utils.test.ts
+++ b/apps/designer/app/shared/tree-utils.test.ts
@@ -3,6 +3,7 @@ import type {
   Instance,
   Prop,
   StyleDecl,
+  Styles,
   StyleSource,
   StyleSourceSelection,
 } from "@webstudio-is/project-build";
@@ -73,7 +74,10 @@ const createStyleSourceSelection = (
   };
 };
 
-const createStyleDecl = (styleSourceId: string): StyleDecl => {
+const createStyleDecl = (
+  styleSourceId: string,
+  breakpointId: string
+): StyleDecl => {
   return {
     styleSourceId,
     breakpointId: "breakpointId",
@@ -389,21 +393,21 @@ test("clone style source selections with applied instance ids and style source i
 });
 
 test("clone styles with appled new style source ids", () => {
-  const styles = [
-    createStyleDecl("styleSource1"),
-    createStyleDecl("styleSource2"),
-    createStyleDecl("styleSource1"),
-    createStyleDecl("styleSource3"),
-    createStyleDecl("styleSource1"),
-    createStyleDecl("styleSource3"),
-  ];
+  const styles: Styles = new Map([
+    [`styleSource1:bp1:width`, createStyleDecl("styleSource1", "bp1")],
+    [`styleSource2:bp2:width`, createStyleDecl("styleSource2", "bp2")],
+    [`styleSource1:bp3:width`, createStyleDecl("styleSource1", "bp3")],
+    [`styleSource3:bp4:width`, createStyleDecl("styleSource3", "bp4")],
+    [`styleSource1:bp5:width`, createStyleDecl("styleSource1", "bp5")],
+    [`styleSource3:bp6:width`, createStyleDecl("styleSource3", "bp6")],
+  ]);
   const clonedStyleSourceIds = new Map<StyleSource["id"], StyleSource["id"]>();
   clonedStyleSourceIds.set("styleSource2", "newStyleSource2");
   clonedStyleSourceIds.set("styleSource3", "newStyleSource3");
   expect(cloneStyles(styles, clonedStyleSourceIds)).toEqual([
-    createStyleDecl("newStyleSource2"),
-    createStyleDecl("newStyleSource3"),
-    createStyleDecl("newStyleSource3"),
+    createStyleDecl("newStyleSource2", "bp2"),
+    createStyleDecl("newStyleSource3", "bp4"),
+    createStyleDecl("newStyleSource3", "bp6"),
   ]);
 });
 
diff --git a/apps/designer/app/shared/tree-utils.ts b/apps/designer/app/shared/tree-utils.ts
index 225f5c6945..d7c5d421a4 100644
--- a/apps/designer/app/shared/tree-utils.ts
+++ b/apps/designer/app/shared/tree-utils.ts
@@ -4,6 +4,7 @@ import type {
   Instance,
   Prop,
   Props,
+  StyleDecl,
   Styles,
   StyleSource,
   StyleSources,
@@ -277,8 +278,8 @@ export const cloneStyles = (
   styles: Styles,
   clonedStyleSourceIds: Map<Instance["id"], Instance["id"]>
 ) => {
-  const clonedStyles: Styles = [];
-  for (const styleDecl of styles) {
+  const clonedStyles: StyleDecl[] = [];
+  for (const styleDecl of styles.values()) {
     const styleSourceId = clonedStyleSourceIds.get(styleDecl.styleSourceId);
     if (styleSourceId === undefined) {
       continue;
diff --git a/packages/project-build/src/schema/styles.ts b/packages/project-build/src/schema/styles.ts
index e75e0440b0..dbd66508ae 100644
--- a/packages/project-build/src/schema/styles.ts
+++ b/packages/project-build/src/schema/styles.ts
@@ -34,6 +34,15 @@ export const StyleDecl = z.object({
 
 export type StyleDecl = z.infer<typeof StyleDecl>;
 
-export const Styles = z.array(StyleDecl);
+export type StyleDeclKey =
+  `${StyleDecl["styleSourceId"]}:${StyleDecl["breakpointId"]}:${StyleDecl["property"]}`;
+
+export const getStyleDeclKey = (
+  styleDecl: Omit<StyleDecl, "value">
+): StyleDeclKey => {
+  return `${styleDecl.styleSourceId}:${styleDecl.breakpointId}:${styleDecl.property}`;
+};
+
+export const Styles = z.map(z.string() as z.ZodType<StyleDeclKey>, StyleDecl);
 
 export type Styles = z.infer<typeof Styles>;
diff --git a/packages/project/src/db/build.ts b/packages/project/src/db/build.ts
index 5c59a591cf..0ef9625445 100644
--- a/packages/project/src/db/build.ts
+++ b/packages/project/src/db/build.ts
@@ -23,7 +23,7 @@ const parseBuild = async (build: DbBuild): Promise<Build> => {
     createdAt: build.createdAt.toISOString(),
     pages,
     breakpoints: Breakpoints.parse(JSON.parse(build.breakpoints)),
-    styles: await parseStyles(build.projectId, build.styles),
+    styles: Array.from(await parseStyles(build.projectId, build.styles)),
     styleSources: Array.from(parseStyleSources(build.styleSources)),
   };
 };
@@ -321,9 +321,9 @@ export async function create(
       breakpoints: JSON.stringify(
         props.sourceBuild?.breakpoints ?? db.breakpoints.createValues()
       ),
-      styles: serializeStyles(props.sourceBuild?.styles ?? []),
+      styles: serializeStyles(new Map(props.sourceBuild?.styles)),
       styleSources: serializeStyleSources(
-        new Map(props.sourceBuild?.styleSources ?? [])
+        new Map(props.sourceBuild?.styleSources)
       ),
       isDev: props.env === "dev",
       isProd: props.env === "prod",
diff --git a/packages/project/src/db/styles.ts b/packages/project/src/db/styles.ts
index 36e45a0c2e..04ea941062 100644
--- a/packages/project/src/db/styles.ts
+++ b/packages/project/src/db/styles.ts
@@ -3,7 +3,13 @@ import { type Patch, applyPatches } from "immer";
 import { prisma } from "@webstudio-is/prisma-client";
 import type { Asset } from "@webstudio-is/asset-uploader";
 import { formatAsset } from "@webstudio-is/asset-uploader/server";
-import { StoredStyles, Styles } from "@webstudio-is/project-build";
+import {
+  type StoredStyleDecl,
+  type StyleDecl,
+  getStyleDeclKey,
+  StoredStyles,
+  Styles,
+} from "@webstudio-is/project-build";
 import type { Build, Project } from "../shared/schema";
 import {
   authorizeProject,
@@ -11,7 +17,7 @@ import {
 } from "@webstudio-is/trpc-interface/server";
 
 const parseValue = (
-  styleValue: StoredStyles[number]["value"],
+  styleValue: StoredStyleDecl["value"],
   assetsMap: Map<string, Asset>
 ) => {
   if (styleValue.type === "image") {
@@ -67,14 +73,16 @@ export const parseStyles = async (
     assetsMap.set(asset.id, formatAsset(asset));
   }
 
-  const styles: Styles = storedStyles.map((styleDecl) => {
-    return {
-      styleSourceId: styleDecl.styleSourceId,
-      breakpointId: styleDecl.breakpointId,
-      property: styleDecl.property,
-      value: parseValue(styleDecl.value, assetsMap),
+  const styles: Styles = new Map();
+  for (const storedStyleDecl of storedStyles) {
+    const styleDecl = {
+      styleSourceId: storedStyleDecl.styleSourceId,
+      breakpointId: storedStyleDecl.breakpointId,
+      property: storedStyleDecl.property,
+      value: parseValue(storedStyleDecl.value, assetsMap),
     };
-  });
+    styles.set(getStyleDeclKey(styleDecl), styleDecl);
+  }
 
   return styles;
 };
@@ -82,7 +90,7 @@ export const parseStyles = async (
 /**
  * prepare value to store in db
  */
-const serializeValue = (styleValue: Styles[number]["value"]) => {
+const serializeValue = (styleValue: StyleDecl["value"]) => {
   if (styleValue.type === "image") {
     return {
       type: "image" as const,
@@ -97,14 +105,17 @@ const serializeValue = (styleValue: Styles[number]["value"]) => {
 };
 
 export const serializeStyles = (styles: Styles) => {
-  const storedStyles: StoredStyles = styles.map((styleDecl) => {
-    return {
-      breakpointId: styleDecl.breakpointId,
-      styleSourceId: styleDecl.styleSourceId,
-      property: styleDecl.property,
-      value: serializeValue(styleDecl.value),
-    };
-  });
+  const storedStyles: StoredStyles = Array.from(
+    styles.values(),
+    (styleDecl) => {
+      return {
+        breakpointId: styleDecl.breakpointId,
+        styleSourceId: styleDecl.styleSourceId,
+        property: styleDecl.property,
+        value: serializeValue(styleDecl.value),
+      };
+    }
+  );
   return JSON.stringify(storedStyles);
 };
 
diff --git a/packages/project/src/shared/schema.ts b/packages/project/src/shared/schema.ts
index 7926d8969c..6ab9b68afa 100644
--- a/packages/project/src/shared/schema.ts
+++ b/packages/project/src/shared/schema.ts
@@ -1,6 +1,10 @@
 import { z, type ZodType } from "zod";
 import type { Breakpoints } from "@webstudio-is/css-data";
-import type { Styles, StyleSource } from "@webstudio-is/project-build";
+import type {
+  StyleDecl,
+  StyleDeclKey,
+  StyleSource,
+} from "@webstudio-is/project-build";
 import type { Data } from "@webstudio-is/react-sdk";
 
 const MIN_TITLE_LENGTH = 2;
@@ -99,7 +103,7 @@ export type Build = {
   isProd: boolean;
   pages: Pages;
   breakpoints: Breakpoints;
-  styles: Styles;
+  styles: [StyleDeclKey, StyleDecl][];
   styleSources: [StyleSource["id"], StyleSource][];
 };
 
diff --git a/packages/project/src/shared/styles/style-rules.test.ts b/packages/project/src/shared/styles/style-rules.test.ts
index 50816bfcf0..a7d0966e80 100644
--- a/packages/project/src/shared/styles/style-rules.test.ts
+++ b/packages/project/src/shared/styles/style-rules.test.ts
@@ -6,50 +6,71 @@ import type {
 import { getStyleRules } from "./style-rules";
 
 test("compute styles from different style sources", () => {
-  const styles: Styles = [
-    {
-      breakpointId: "a",
-      styleSourceId: "styleSource1",
-      property: "width",
-      value: { type: "unit", value: 10, unit: "px" },
-    },
-    {
-      breakpointId: "a",
-      styleSourceId: "styleSource2",
-      property: "display",
-      value: { type: "keyword", value: "block" },
-    },
-    {
-      breakpointId: "a",
-      styleSourceId: "styleSource4",
-      property: "color",
-      value: { type: "keyword", value: "green" },
-    },
-    {
-      breakpointId: "a",
-      styleSourceId: "styleSource4",
-      property: "width",
-      value: { type: "keyword", value: "min-content" },
-    },
-    {
-      breakpointId: "a",
-      styleSourceId: "styleSource3",
-      property: "color",
-      value: { type: "keyword", value: "red" },
-    },
-    {
-      breakpointId: "b",
-      styleSourceId: "styleSource5",
-      property: "color",
-      value: { type: "keyword", value: "orange" },
-    },
-    {
-      breakpointId: "a",
-      styleSourceId: "styleSource6",
-      property: "color",
-      value: { type: "keyword", value: "blue" },
-    },
-  ];
+  const styles: Styles = new Map([
+    [
+      "styleSource1:a:width",
+      {
+        breakpointId: "a",
+        styleSourceId: "styleSource1",
+        property: "width",
+        value: { type: "unit", value: 10, unit: "px" },
+      },
+    ],
+    [
+      "styleSource2:a:display",
+      {
+        breakpointId: "a",
+        styleSourceId: "styleSource2",
+        property: "display",
+        value: { type: "keyword", value: "block" },
+      },
+    ],
+    [
+      "styleSource4:a:color",
+      {
+        breakpointId: "a",
+        styleSourceId: "styleSource4",
+        property: "color",
+        value: { type: "keyword", value: "green" },
+      },
+    ],
+    [
+      "styleSource4:a:width",
+      {
+        breakpointId: "a",
+        styleSourceId: "styleSource4",
+        property: "width",
+        value: { type: "keyword", value: "min-content" },
+      },
+    ],
+    [
+      "styleSource3:a:color",
+      {
+        breakpointId: "a",
+        styleSourceId: "styleSource3",
+        property: "color",
+        value: { type: "keyword", value: "red" },
+      },
+    ],
+    [
+      "styleSource5:b:color",
+      {
+        breakpointId: "b",
+        styleSourceId: "styleSource5",
+        property: "color",
+        value: { type: "keyword", value: "orange" },
+      },
+    ],
+    [
+      "styleSource6:a:color",
+      {
+        breakpointId: "a",
+        styleSourceId: "styleSource6",
+        property: "color",
+        value: { type: "keyword", value: "blue" },
+      },
+    ],
+  ]);
   const styleSourceSelections: StyleSourceSelections = new Map([
     [
       "instance1",
diff --git a/packages/project/src/shared/styles/style-rules.ts b/packages/project/src/shared/styles/style-rules.ts
index 4d7e7cc1d1..8f68e95aab 100644
--- a/packages/project/src/shared/styles/style-rules.ts
+++ b/packages/project/src/shared/styles/style-rules.ts
@@ -1,5 +1,6 @@
 import type { Breakpoint, Style } from "@webstudio-is/css-data";
 import type {
+  StyleDecl,
   Styles,
   StyleSource,
   StyleSourceSelections,
@@ -16,14 +17,14 @@ type StyleRule = {
  * and group by instance and breakpoint
  */
 export const getStyleRules = (
-  styles?: Styles,
-  styleSourceSelections?: StyleSourceSelections
+  styles: Styles,
+  styleSourceSelections: StyleSourceSelections
 ) => {
   if (styles === undefined || styleSourceSelections === undefined) {
     return [];
   }
-  const stylesByStyleSourceId = new Map<StyleSource["id"], Styles>();
-  for (const styleDecl of styles) {
+  const stylesByStyleSourceId = new Map<StyleSource["id"], StyleDecl[]>();
+  for (const styleDecl of styles.values()) {
     const { styleSourceId } = styleDecl;
     let styleSourceStyles = stylesByStyleSourceId.get(styleSourceId);
     // instance can be undefined when style is from other tree