diff --git a/crates/swc_css_codegen/src/lib.rs b/crates/swc_css_codegen/src/lib.rs
index ad29d732d4de..db2db4d50f0f 100644
--- a/crates/swc_css_codegen/src/lib.rs
+++ b/crates/swc_css_codegen/src/lib.rs
@@ -2763,9 +2763,9 @@ fn minify_hex_color(value: &str) -> String {
             if length == 6 || chars[6] == b'f' && chars[7] == b'f' {
                 let mut minified = String::with_capacity(3);
 
-                minified.push((chars[0] as char).to_ascii_lowercase());
-                minified.push((chars[2] as char).to_ascii_lowercase());
-                minified.push((chars[4] as char).to_ascii_lowercase());
+                minified.push(chars[0] as char);
+                minified.push(chars[2] as char);
+                minified.push(chars[4] as char);
 
                 return minified;
             }
@@ -2773,17 +2773,17 @@ fn minify_hex_color(value: &str) -> String {
             else if length == 8 && chars[6] == chars[7] {
                 let mut minified = String::with_capacity(4);
 
-                minified.push((chars[0] as char).to_ascii_lowercase());
-                minified.push((chars[2] as char).to_ascii_lowercase());
-                minified.push((chars[4] as char).to_ascii_lowercase());
-                minified.push((chars[6] as char).to_ascii_lowercase());
+                minified.push(chars[0] as char);
+                minified.push(chars[2] as char);
+                minified.push(chars[4] as char);
+                minified.push(chars[6] as char);
 
                 return minified;
             }
         }
     }
 
-    value.to_ascii_lowercase()
+    value.to_string()
 }
 
 fn serialize_string(value: &str) -> String {
diff --git a/crates/swc_css_minifier/src/compressor/declaration.rs b/crates/swc_css_minifier/src/compressor/declaration.rs
index b53b9ef34140..2f48ed995be9 100644
--- a/crates/swc_css_minifier/src/compressor/declaration.rs
+++ b/crates/swc_css_minifier/src/compressor/declaration.rs
@@ -6,8 +6,8 @@ use super::Compressor;
 
 impl Compressor {
     pub(super) fn compress_declaration(&self, declaration: &mut Declaration) {
-        if let DeclarationName::Ident(Ident { value, .. }) = &declaration.name {
-            match value.to_ascii_lowercase() {
+        if let DeclarationName::Ident(Ident { value: name, .. }) = &declaration.name {
+            match *name {
                 js_word!("display") if declaration.value.len() > 1 => {
                     let mut outside = None;
                     let mut inside = None;
@@ -616,12 +616,12 @@ impl Compressor {
 
     fn compress_from_initial(&self, declaration: &mut Declaration, span: Span) {
         let name = if let DeclarationName::Ident(Ident { value, .. }) = &declaration.name {
-            value.to_ascii_lowercase()
+            value
         } else {
             return;
         };
 
-        match name {
+        match *name {
             js_word!("accent-color")
             | js_word!("align-self")
             | js_word!("animation-timeline")
@@ -1282,12 +1282,12 @@ impl Compressor {
 
     fn _compress_to_initial(&self, declaration: &mut Declaration) {
         let name = if let DeclarationName::Ident(Ident { value, .. }) = &declaration.name {
-            value.to_ascii_lowercase()
+            value
         } else {
             return;
         };
 
-        match name {
+        match *name {
             js_word!("background-clip") | js_word!("mask-clip") | js_word!("mask-origin") => {
                 if let Some(ComponentValue::Ident(box Ident { value, span, .. })) =
                     declaration.value.get(0)
diff --git a/crates/swc_css_modules/src/lib.rs b/crates/swc_css_modules/src/lib.rs
index bd69c4fd9285..443ca501c381 100644
--- a/crates/swc_css_modules/src/lib.rs
+++ b/crates/swc_css_modules/src/lib.rs
@@ -316,7 +316,7 @@ where
         }
 
         if let DeclarationName::Ident(name) = &n.name {
-            match name.value.to_ascii_lowercase() {
+            match name.value {
                 js_word!("animation") => {
                     let mut can_change = true;
 
diff --git a/crates/swc_css_parser/src/parser/syntax/mod.rs b/crates/swc_css_parser/src/parser/syntax/mod.rs
index 9efae7729416..9f22658e622e 100644
--- a/crates/swc_css_parser/src/parser/syntax/mod.rs
+++ b/crates/swc_css_parser/src/parser/syntax/mod.rs
@@ -613,7 +613,11 @@ where
         let name = if is_dashed_ident {
             DeclarationName::DashedIdent(self.parse()?)
         } else {
-            DeclarationName::Ident(self.parse()?)
+            let mut ident: Ident = self.parse()?;
+
+            ident.value = ident.value.to_ascii_lowercase();
+
+            DeclarationName::Ident(ident)
         };
         let mut declaration = Declaration {
             span: Default::default(),
@@ -742,7 +746,7 @@ where
             };
             let value = Ident {
                 span: important_ident.span,
-                value: value.0,
+                value: value.0.to_ascii_lowercase(),
                 raw: Some(value.1),
             };
 
diff --git a/crates/swc_css_parser/tests/fixture/at-rule/import/output.json b/crates/swc_css_parser/tests/fixture/at-rule/import/output.json
index 0251ea8ee94d..4337a9fcdd16 100644
--- a/crates/swc_css_parser/tests/fixture/at-rule/import/output.json
+++ b/crates/swc_css_parser/tests/fixture/at-rule/import/output.json
@@ -9257,7 +9257,7 @@
                     "end": 4781,
                     "ctxt": 0
                   },
-                  "value": "DISPLAY",
+                  "value": "display",
                   "raw": "DISPLAY"
                 },
                 "value": [
diff --git a/crates/swc_css_parser/tests/fixture/important/basic/output.json b/crates/swc_css_parser/tests/fixture/important/basic/output.json
index 7ffa61813383..096b388f3872 100644
--- a/crates/swc_css_parser/tests/fixture/important/basic/output.json
+++ b/crates/swc_css_parser/tests/fixture/important/basic/output.json
@@ -453,7 +453,7 @@
                   "end": 219,
                   "ctxt": 0
                 },
-                "value": "IMPORTANT",
+                "value": "important",
                 "raw": "IMPORTANT"
               }
             }
@@ -501,7 +501,7 @@
                   "end": 251,
                   "ctxt": 0
                 },
-                "value": "IMPORTANT",
+                "value": "important",
                 "raw": "IMPORTANT"
               }
             }
@@ -930,7 +930,7 @@
                   "end": 519,
                   "ctxt": 0
                 },
-                "value": "iMpOrTaNt",
+                "value": "important",
                 "raw": "iMpOrTaNt"
               }
             }
diff --git a/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/output.json b/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/output.json
index e9825b1f0028..fed665b0414a 100644
--- a/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/output.json
+++ b/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/output.json
@@ -651,7 +651,7 @@
                       "end": 234,
                       "ctxt": 0
                     },
-                    "value": "CONTENT",
+                    "value": "content",
                     "raw": "CONTENT"
                   },
                   "value": [
@@ -685,7 +685,7 @@
                 "end": 255,
                 "ctxt": 0
               },
-              "value": "MARGIN-LEFT",
+              "value": "margin-left",
               "raw": "MARGIN-LEFT"
             },
             "value": [
diff --git a/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/page-properties-case-insensitive/output.json b/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/page-properties-case-insensitive/output.json
index 3f223676c08b..4d85a7d2da6c 100644
--- a/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/page-properties-case-insensitive/output.json
+++ b/crates/swc_css_parser/tests/fixture/vendor/rome/at-page/page-properties-case-insensitive/output.json
@@ -55,7 +55,7 @@
                 "end": 17,
                 "ctxt": 0
               },
-              "value": "DISPLAY",
+              "value": "display",
               "raw": "DISPLAY"
             },
             "value": [
diff --git a/crates/swc_css_prefixer/src/prefixer.rs b/crates/swc_css_prefixer/src/prefixer.rs
index dc8ce0334cb1..415eb3623ec8 100644
--- a/crates/swc_css_prefixer/src/prefixer.rs
+++ b/crates/swc_css_prefixer/src/prefixer.rs
@@ -1594,7 +1594,7 @@ impl VisitMut for Prefixer {
             }};
         }
 
-        let property_name = &*name.to_ascii_lowercase();
+        let property_name: &str = name;
 
         match property_name {
             "appearance" => {
diff --git a/crates/swc_css_prefixer/tests/fixture/case-insensivity/input.css b/crates/swc_css_prefixer/tests/fixture/case-insensivity/input.css
index 80b91b694d31..96593ae3a428 100644
--- a/crates/swc_css_prefixer/tests/fixture/case-insensivity/input.css
+++ b/crates/swc_css_prefixer/tests/fixture/case-insensivity/input.css
@@ -5,3 +5,13 @@ a {
 b {
     APPEARANCE: AUTO;
 }
+
+c {
+    -WEBKIT-APPEARANCE: NONE;
+    APPEARANCE: NONE;
+}
+
+d {
+    -webkit-appearance: NONE;
+    APPEARANCE: NONE;
+}
\ No newline at end of file
diff --git a/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.css b/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.css
index de15328a342e..5297ce26839c 100644
--- a/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.css
+++ b/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.css
@@ -10,3 +10,15 @@ b {
   -ms-appearance: AUTO;
   APPEARANCE: AUTO;
 }
+c {
+  -WEBKIT-APPEARANCE: NONE;
+  -moz-appearance: NONE;
+  -ms-appearance: NONE;
+  APPEARANCE: NONE;
+}
+d {
+  -webkit-appearance: NONE;
+  -moz-appearance: NONE;
+  -ms-appearance: NONE;
+  APPEARANCE: NONE;
+}
diff --git a/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.defaults-not-ie-11.css b/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.defaults-not-ie-11.css
index 75ea68262bf8..21d6ccb5f65c 100644
--- a/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.defaults-not-ie-11.css
+++ b/crates/swc_css_prefixer/tests/fixture/case-insensivity/output.defaults-not-ie-11.css
@@ -6,3 +6,11 @@ b {
   -webkit-appearance: AUTO;
   APPEARANCE: AUTO;
 }
+c {
+  -WEBKIT-APPEARANCE: NONE;
+  APPEARANCE: NONE;
+}
+d {
+  -webkit-appearance: NONE;
+  APPEARANCE: NONE;
+}