diff --git a/.changeset/dry-eggs-retire.md b/.changeset/dry-eggs-retire.md
new file mode 100644
index 0000000000..1e8bb95d75
--- /dev/null
+++ b/.changeset/dry-eggs-retire.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: improve style parser whitespace handling
diff --git a/packages/svelte/src/compiler/phases/1-parse/read/style.js b/packages/svelte/src/compiler/phases/1-parse/read/style.js
index 600c10f33a..545542d80f 100644
--- a/packages/svelte/src/compiler/phases/1-parse/read/style.js
+++ b/packages/svelte/src/compiler/phases/1-parse/read/style.js
@@ -7,7 +7,7 @@ const REGEX_COMBINATOR_WHITESPACE = /^\s*(\+|~|>|\|\|)\s*/;
 const REGEX_COMBINATOR = /^(\+|~|>|\|\|)/;
 const REGEX_PERCENTAGE = /^\d+(\.\d+)?%/;
 const REGEX_NTH_OF =
-	/^\s*(even|odd|\+?(\d+|\d*n(\s*[+-]\s*\d+)?)|-\d*n(\s*\+\s*\d+))(\s*(?=[,)])|\s+of\s+)/;
+	/^(even|odd|\+?(\d+|\d*n(\s*[+-]\s*\d+)?)|-\d*n(\s*\+\s*\d+))((?=\s*[,)])|\s+of\s+)/;
 const REGEX_WHITESPACE_OR_COLON = /[\s:]/;
 const REGEX_BRACE_OR_SEMICOLON = /[{;]/;
 const REGEX_LEADING_HYPHEN_OR_DIGIT = /-?\d/;
@@ -153,6 +153,8 @@ function read_selector_list(parser, inside_pseudo_class = false) {
 	/** @type {import('#compiler').Css.Selector[]} */
 	const children = [];
 
+	allow_comment_or_whitespace(parser);
+
 	const start = parser.index;
 
 	while (parser.index < parser.template.length) {
@@ -286,9 +288,10 @@ function read_selector(parser, inside_pseudo_class = false) {
 			});
 		} else if (inside_pseudo_class && parser.match_regex(REGEX_NTH_OF)) {
 			// nth of matcher must come before combinator matcher to prevent collision else the '+' in '+2n-1' would be parsed as a combinator
+
 			children.push({
 				type: 'Nth',
-				value: /** @type {string} */ (parser.read(REGEX_NTH_OF)),
+				value: /**@type {string} */ (parser.read(REGEX_NTH_OF)),
 				start,
 				end: parser.index
 			});
diff --git a/packages/svelte/tests/parser-modern/samples/css-nth-syntax/output.json b/packages/svelte/tests/parser-modern/samples/css-nth-syntax/output.json
index 87ab7c02eb..9e13a7cb86 100644
--- a/packages/svelte/tests/parser-modern/samples/css-nth-syntax/output.json
+++ b/packages/svelte/tests/parser-modern/samples/css-nth-syntax/output.json
@@ -495,19 +495,19 @@
 									"name": "nth-child",
 									"args": {
 										"type": "SelectorList",
-										"start": 476,
-										"end": 491,
+										"start": 485,
+										"end": 486,
 										"children": [
 											{
 												"type": "Selector",
-												"start": 476,
-												"end": 491,
+												"start": 485,
+												"end": 486,
 												"children": [
 													{
 														"type": "Nth",
-														"value": "\n        n\n    ",
-														"start": 476,
-														"end": 491
+														"value": "n",
+														"start": 485,
+														"end": 486
 													}
 												]
 											}
diff --git a/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/input.svelte b/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/input.svelte
index 6602f9c044..d8ed0f9e36 100644
--- a/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/input.svelte
+++ b/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/input.svelte
@@ -15,4 +15,10 @@
 	::slotted(.content) {
 		color: red;
 	}
+	:is( /*button*/
+		button, /*p after h1*/
+		h1 + p
+		){
+		color: red;
+	}
 </style>
diff --git a/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/output.json b/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/output.json
index f502060e13..1431b123a4 100644
--- a/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/output.json
+++ b/packages/svelte/tests/parser-modern/samples/css-pseudo-classes/output.json
@@ -2,7 +2,7 @@
 	"css": {
 		"type": "Style",
 		"start": 0,
-		"end": 313,
+		"end": 386,
 		"attributes": [],
 		"children": [
 			{
@@ -225,12 +225,96 @@
 				},
 				"start": 266,
 				"end": 304
+			},
+			{
+				"type": "Rule",
+				"prelude": {
+					"type": "SelectorList",
+					"start": 306,
+					"end": 359,
+					"children": [
+						{
+							"type": "Selector",
+							"start": 306,
+							"end": 359,
+							"children": [
+								{
+									"type": "PseudoClassSelector",
+									"name": "is",
+									"args": {
+										"type": "SelectorList",
+										"start": 324,
+										"end": 355,
+										"children": [
+											{
+												"type": "Selector",
+												"start": 324,
+												"end": 330,
+												"children": [
+													{
+														"type": "TypeSelector",
+														"name": "button",
+														"start": 324,
+														"end": 330
+													}
+												]
+											},
+											{
+												"type": "Selector",
+												"start": 349,
+												"end": 355,
+												"children": [
+													{
+														"type": "TypeSelector",
+														"name": "h1",
+														"start": 349,
+														"end": 351
+													},
+													{
+														"type": "Combinator",
+														"name": "+",
+														"start": 352,
+														"end": 353
+													},
+													{
+														"type": "TypeSelector",
+														"name": "p",
+														"start": 354,
+														"end": 355
+													}
+												]
+											}
+										]
+									},
+									"start": 306,
+									"end": 359
+								}
+							]
+						}
+					]
+				},
+				"block": {
+					"type": "Block",
+					"start": 359,
+					"end": 377,
+					"children": [
+						{
+							"type": "Declaration",
+							"start": 363,
+							"end": 373,
+							"property": "color",
+							"value": "red"
+						}
+					]
+				},
+				"start": 306,
+				"end": 377
 			}
 		],
 		"content": {
 			"start": 7,
-			"end": 305,
-			"styles": "\n    /* test that all these are parsed correctly */\n\t::view-transition-old(x-y)  {\n\t\tcolor: red;\n    }\n\t:global(::view-transition-old(x-y))  {\n\t\tcolor: red;\n    }\n\t::highlight(rainbow-color-1) {\n\t\tcolor: red;\n\t}\n\tcustom-element::part(foo) {\n\t\tcolor: red;\n\t}\n\t::slotted(.content) {\n\t\tcolor: red;\n\t}\n"
+			"end": 378,
+			"styles": "\n    /* test that all these are parsed correctly */\n\t::view-transition-old(x-y)  {\n\t\tcolor: red;\n    }\n\t:global(::view-transition-old(x-y))  {\n\t\tcolor: red;\n    }\n\t::highlight(rainbow-color-1) {\n\t\tcolor: red;\n\t}\n\tcustom-element::part(foo) {\n\t\tcolor: red;\n\t}\n\t::slotted(.content) {\n\t\tcolor: red;\n\t}\n\t:is( /*button*/\n\t\tbutton, /*p after h1*/\n\t\th1 + p\n\t\t){\n\t\tcolor: red;\n\t}\n"
 		}
 	},
 	"js": [],