diff --git a/lib/css/CssParser.js b/lib/css/CssParser.js
index 33383eaa699..2e6a0878183 100644
--- a/lib/css/CssParser.js
+++ b/lib/css/CssParser.js
@@ -279,8 +279,8 @@ class CssParser extends Parser {
 				module.addDependency(dep);
 				declaredCssVariables.add(name);
 			} else if (
-				propertyName === "animation-name" ||
-				propertyName === "animation"
+				propertyName.toLowerCase() === "animation-name" ||
+				propertyName.toLowerCase() === "animation"
 			) {
 				modeData = "animation";
 				lastIdentifier = undefined;
@@ -343,7 +343,7 @@ class CssParser extends Parser {
 				return end;
 			},
 			atKeyword: (input, start, end) => {
-				const name = input.slice(start, end);
+				const name = input.slice(start, end).toLowerCase();
 				if (name === "@namespace") {
 					throw new Error("@namespace is not supported in bundled CSS");
 				}
@@ -543,7 +543,7 @@ class CssParser extends Parser {
 				singleClassSelector = false;
 				switch (mode) {
 					case CSS_MODE_TOP_LEVEL: {
-						const name = input.slice(start, end);
+						const name = input.slice(start, end).toLowerCase();
 						if (this.allowModeSwitch && name === ":global") {
 							modeData = "global";
 							const dep = new ConstDependency("", [start, end]);
@@ -566,7 +566,7 @@ class CssParser extends Parser {
 			pseudoFunction: (input, start, end) => {
 				switch (mode) {
 					case CSS_MODE_TOP_LEVEL: {
-						const name = input.slice(start, end - 1);
+						const name = input.slice(start, end - 1).toLowerCase();
 						if (this.allowModeSwitch && name === ":global") {
 							modeStack.push(modeData);
 							modeData = "global";
@@ -589,7 +589,7 @@ class CssParser extends Parser {
 			function: (input, start, end) => {
 				switch (mode) {
 					case CSS_MODE_IN_LOCAL_RULE: {
-						const name = input.slice(start, end - 1);
+						const name = input.slice(start, end - 1).toLowerCase();
 						if (name === "var") {
 							let pos = walkCssTokens.eatWhitespaceAndComments(input, end);
 							if (pos === input.length) return pos;
diff --git a/lib/css/walkCssTokens.js b/lib/css/walkCssTokens.js
index 6ba1dcaabb3..26276b10a43 100644
--- a/lib/css/walkCssTokens.js
+++ b/lib/css/walkCssTokens.js
@@ -62,6 +62,7 @@ const CC_LOWER_E = "e".charCodeAt(0);
 const CC_LOWER_Z = "z".charCodeAt(0);
 const CC_UPPER_A = "A".charCodeAt(0);
 const CC_UPPER_E = "E".charCodeAt(0);
+const CC_UPPER_U = "U".charCodeAt(0);
 const CC_UPPER_Z = "Z".charCodeAt(0);
 const CC_0 = "0".charCodeAt(0);
 const CC_9 = "9".charCodeAt(0);
@@ -288,7 +289,10 @@ const consumeOtherIdentifier = (input, pos, callbacks) => {
 const consumePotentialUrl = (input, pos, callbacks) => {
 	const start = pos;
 	pos = _consumeIdentifier(input, pos);
-	if (pos === start + 3 && input.slice(start, pos + 1) === "url(") {
+	if (
+		pos === start + 3 &&
+		input.slice(start, pos + 1).toLowerCase() === "url("
+	) {
 		pos++;
 		let cc = input.charCodeAt(pos);
 		while (_isWhiteSpace(cc)) {
@@ -569,6 +573,7 @@ const CHAR_MAP = Array.from({ length: 0x80 }, (_, cc) => {
 		case CC_AT_SIGN:
 			return consumeAt;
 		case CC_LOWER_U:
+		case CC_UPPER_U:
 			return consumePotentialUrl;
 		case CC_LOW_LINE:
 			return consumeOtherIdentifier;
diff --git a/test/__snapshots__/ConfigCacheTestCases.longtest.js.snap b/test/__snapshots__/ConfigCacheTestCases.longtest.js.snap
index 417c4bbfd68..af7e390a3dc 100644
--- a/test/__snapshots__/ConfigCacheTestCases.longtest.js.snap
+++ b/test/__snapshots__/ConfigCacheTestCases.longtest.js.snap
@@ -15,6 +15,8 @@ Object {
   "j": " green url(img\\\\ img.09a1a1112c577c279435.png) xyz",
   "k": " green url(img\\\\ img.09a1a1112c577c279435.png) xyz",
   "l": " green url(img.09a1a1112c577c279435.png) xyz",
+  "m": " green url(img.09a1a1112c577c279435.png) xyz",
+  "n": " green url(img.09a1a1112c577c279435.png) xyz",
 }
 `;
 
diff --git a/test/__snapshots__/ConfigTestCases.basictest.js.snap b/test/__snapshots__/ConfigTestCases.basictest.js.snap
index d475303c830..55b67fa8c54 100644
--- a/test/__snapshots__/ConfigTestCases.basictest.js.snap
+++ b/test/__snapshots__/ConfigTestCases.basictest.js.snap
@@ -15,6 +15,8 @@ Object {
   "j": " green url(img\\\\ img.09a1a1112c577c279435.png) xyz",
   "k": " green url(img\\\\ img.09a1a1112c577c279435.png) xyz",
   "l": " green url(img.09a1a1112c577c279435.png) xyz",
+  "m": " green url(img.09a1a1112c577c279435.png) xyz",
+  "n": " green url(img.09a1a1112c577c279435.png) xyz",
 }
 `;
 
diff --git a/test/configCases/css/css-modules-in-node/index.js b/test/configCases/css/css-modules-in-node/index.js
index e7b6603297b..ffebb43946a 100644
--- a/test/configCases/css/css-modules-in-node/index.js
+++ b/test/configCases/css/css-modules-in-node/index.js
@@ -53,6 +53,18 @@ it("should allow to create css modules", done => {
 				supportsInMedia: prod
 					? "my-app-491-SQ"
 					: "./style.module.css-displayFlexInSupportsInMedia",
+				displayFlexInSupportsInMediaUpperCase: prod
+					? "my-app-491-XM"
+					: "./style.module.css-displayFlexInSupportsInMediaUpperCase",
+				keyframesUPPERCASE: prod
+					? "my-app-491-T4"
+					: "./style.module.css-localkeyframesUPPERCASE",
+				localkeyframes2UPPPERCASE: prod
+					? "my-app-491-Xi"
+					: "./style.module.css-localkeyframes2UPPPERCASE",
+				VARS: prod
+					? "--my-app-491-DJ my-app-491-ms undefined my-app-491-cU"
+					: "--./style.module.css-LOCAL-COLOR ./style.module.css-VARS undefined ./style.module.css-globalVarsUpperCase",
 			});
 		} catch (e) {
 			return done(e);
diff --git a/test/configCases/css/css-modules/index.js b/test/configCases/css/css-modules/index.js
index 8fb2375c18e..1f81266de43 100644
--- a/test/configCases/css/css-modules/index.js
+++ b/test/configCases/css/css-modules/index.js
@@ -56,6 +56,18 @@ it("should allow to create css modules", done => {
 				supportsInMedia: prod
 					? "my-app-491-SQ"
 					: "./style.module.css-displayFlexInSupportsInMedia",
+				displayFlexInSupportsInMediaUpperCase: prod
+					? "my-app-491-XM"
+					: "./style.module.css-displayFlexInSupportsInMediaUpperCase",
+				keyframesUPPERCASE: prod
+					? "my-app-491-T4"
+					: "./style.module.css-localkeyframesUPPERCASE",
+				localkeyframes2UPPPERCASE: prod
+					? "my-app-491-Xi"
+					: "./style.module.css-localkeyframes2UPPPERCASE",
+				VARS: prod
+					? "--my-app-491-DJ my-app-491-ms undefined my-app-491-cU"
+					: "--./style.module.css-LOCAL-COLOR ./style.module.css-VARS undefined ./style.module.css-globalVarsUpperCase",
 			});
 		} catch (e) {
 			return done(e);
diff --git a/test/configCases/css/css-modules/style.module.css b/test/configCases/css/css-modules/style.module.css
index 8e98a3db9a2..da1dc236bf1 100644
--- a/test/configCases/css/css-modules/style.module.css
+++ b/test/configCases/css/css-modules/style.module.css
@@ -166,3 +166,56 @@
     }
   }
 }
+
+@MEDIA screen and (min-width: 900px) {
+	@SUPPORTS (display: flex) {
+		.displayFlexInSupportsInMediaUpperCase {
+			display: flex;
+		}
+	}
+}
+
+.animationUpperCase {
+	ANIMATION-NAME: localkeyframesUPPERCASE;
+	ANIMATION: 3s ease-in 1s 2 reverse both paused localkeyframesUPPERCASE, localkeyframes2UPPPERCASE;
+	--pos1x: 0px;
+	--pos1y: 0px;
+	--pos2x: 10px;
+	--pos2y: 20px;
+}
+
+@KEYFRAMES localkeyframesUPPERCASE {
+	0% {
+		left: VAR(--pos1x);
+		top: VAR(--pos1y);
+		color: VAR(--theme-color1);
+	}
+	100% {
+		left: VAR(--pos2x);
+		top: VAR(--pos2y);
+		color: VAR(--theme-color2);
+	}
+}
+
+@KEYframes localkeyframes2UPPPERCASE {
+	0% {
+		left: 0;
+	}
+	100% {
+		left: 100px;
+	}
+}
+
+:GLOBAL .globalUpperCase :LOCAL .localUpperCase {
+	color: yellow;
+}
+
+.VARS {
+	color: VAR(--LOCAL-COLOR);
+	--LOCAL-COLOR: red;
+}
+
+.globalVarsUpperCase :GLOBAL {
+	COLOR: VAR(--GLOBAR-COLOR);
+	--GLOBAR-COLOR: red;
+}
diff --git a/test/configCases/css/css-modules/use-style.js b/test/configCases/css/css-modules/use-style.js
index e3f624a9991..9013436b2cb 100644
--- a/test/configCases/css/css-modules/use-style.js
+++ b/test/configCases/css/css-modules/use-style.js
@@ -19,6 +19,8 @@ export default {
 	webkitAnyWmultiParams: `${style.local16}`,
 	ident,
 	keyframes: style.localkeyframes,
+	keyframesUPPERCASE: style.localkeyframesUPPERCASE,
+	localkeyframes2UPPPERCASE: style.localkeyframes2UPPPERCASE,
 	animation: style.animation,
 	vars: `${style["local-color"]} ${style.vars} ${style["global-color"]} ${style.globalVars}`,
 	media: style.wideScreenClass,
@@ -27,4 +29,6 @@ export default {
 	supportsWithOperator: style.floatRightInNegativeSupports,
 	mediaInSupports: style.displayFlexInMediaInSupports,
 	supportsInMedia: style.displayFlexInSupportsInMedia,
+	displayFlexInSupportsInMediaUpperCase: style.displayFlexInSupportsInMediaUpperCase,
+	VARS: `${style["LOCAL-COLOR"]} ${style.VARS} ${style["GLOBAL-COLOR"]} ${style.globalVarsUpperCase}`,
 };
diff --git a/test/configCases/css/css-modules/warnings.js b/test/configCases/css/css-modules/warnings.js
index 36ade9aede3..8052a28b9e3 100644
--- a/test/configCases/css/css-modules/warnings.js
+++ b/test/configCases/css/css-modules/warnings.js
@@ -2,7 +2,9 @@ module.exports = [
 	[/export 'global' \(imported as 'style'\) was not found/],
 	[/export 'nested2' \(imported as 'style'\) was not found/],
 	[/export 'global-color' \(imported as 'style'\) was not found/],
+	[/export 'GLOBAL-COLOR' \(imported as 'style'\) was not found/],
 	[/export 'global' \(imported as 'style'\) was not found/],
 	[/export 'nested2' \(imported as 'style'\) was not found/],
-	[/export 'global-color' \(imported as 'style'\) was not found/]
+	[/export 'global-color' \(imported as 'style'\) was not found/],
+	[/export 'GLOBAL-COLOR' \(imported as 'style'\) was not found/]
 ];
diff --git a/test/configCases/css/import-different-case/index.js b/test/configCases/css/import-different-case/index.js
new file mode 100644
index 00000000000..652fef343dd
--- /dev/null
+++ b/test/configCases/css/import-different-case/index.js
@@ -0,0 +1,8 @@
+import * as style from "./style.css";
+
+it("should compile and load style on demand", () => {
+	expect(style).toEqual(nsObj({}));
+	const computedStyle = getComputedStyle(document.body);
+	expect(computedStyle.getPropertyValue("background")).toBe(" red");
+	expect(computedStyle.getPropertyValue("margin")).toBe(" 10px");
+});
diff --git a/test/configCases/css/import-different-case/style-imported.css b/test/configCases/css/import-different-case/style-imported.css
new file mode 100644
index 00000000000..eb0ae451455
--- /dev/null
+++ b/test/configCases/css/import-different-case/style-imported.css
@@ -0,0 +1,3 @@
+body {
+	margin: 10px;
+}
diff --git a/test/configCases/css/import-different-case/style.css b/test/configCases/css/import-different-case/style.css
new file mode 100644
index 00000000000..602ea2d5aa8
--- /dev/null
+++ b/test/configCases/css/import-different-case/style.css
@@ -0,0 +1,4 @@
+@IMPORT "style-imported.css";
+body {
+	background: red;
+}
diff --git a/test/configCases/css/import-different-case/test.config.js b/test/configCases/css/import-different-case/test.config.js
new file mode 100644
index 00000000000..0590757288f
--- /dev/null
+++ b/test/configCases/css/import-different-case/test.config.js
@@ -0,0 +1,8 @@
+module.exports = {
+	moduleScope(scope) {
+		const link = scope.window.document.createElement("link");
+		link.rel = "stylesheet";
+		link.href = "bundle0.css";
+		scope.window.document.head.appendChild(link);
+	}
+};
diff --git a/test/configCases/css/import-different-case/webpack.config.js b/test/configCases/css/import-different-case/webpack.config.js
new file mode 100644
index 00000000000..cfb8e5c0346
--- /dev/null
+++ b/test/configCases/css/import-different-case/webpack.config.js
@@ -0,0 +1,8 @@
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	target: "web",
+	mode: "development",
+	experiments: {
+		css: true
+	}
+};
diff --git a/test/configCases/css/urls/spacing.css b/test/configCases/css/urls/spacing.css
index 424db230184..21f5c3e982a 100644
--- a/test/configCases/css/urls/spacing.css
+++ b/test/configCases/css/urls/spacing.css
@@ -47,3 +47,11 @@ spacing {
 spacing {
   l: green url(/img.png) xyz;
 }
+
+spacing {
+	m: green URL(/img.png) xyz;
+}
+
+spacing {
+	n: green uRl(/img.png) xyz;
+}