fix: prefer relative

lib/config/defaults.js

@@ -1435,12 +1435,14 @@ const getResolveDefaults = ({ cache, context, targetProperties, mode }) => {
 		extensions: [...jsExtensions]
 	});
 
+	const cssExtensions = [".css"];
+
 	/** @type {function(): ResolveOptions} */
 	const styleDeps = () => ({
 		mainFields: ["style", "..."],
 		mainFiles: [],
 		conditionNames: ["style"],
-		extensions: [".css"]
+		extensions: [...cssExtensions]
 	});
 
 	/** @type {ResolveOptions} */
@@ -1473,7 +1475,10 @@ const getResolveDefaults = ({ cache, context, targetProperties, mode }) => {
 			unknown: cjsDeps(),
 			// for backward-compat: getResolve without dependencyType
 			undefined: cjsDeps(),
-			"css-import": styleDeps()
+			"css-import": {
+				...styleDeps(),
+				preferRelative: true
+			}
 		}
 	};
 

test/configCases/css/css-import/node_modules/prefer-relative.css/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "prefer-relative.css",
+  "style": "./styles.css"
+}

test/configCases/css/css-import/node_modules/prefer-relative.css/styles.css

@@ -0,0 +1,3 @@
+.should-be-not-imported {
+	color: steelblue;
+}

test/configCases/css/css-import/prefer-relative.css

@@ -0,0 +1,3 @@
+.relative {
+	color: red;
+}

test/configCases/css/css-import/style-import.css

@@ -7,3 +7,4 @@
 @import "./directory";
 @import "./extensions-imported.mycss";
 @import "./with-less-import.css";
+@import "prefer-relative.css";