diff --git a/packages/language-server/src/lib/documents/parseHtml.ts b/packages/language-server/src/lib/documents/parseHtml.ts
index 94b8810e3..6441b8fc0 100644
--- a/packages/language-server/src/lib/documents/parseHtml.ts
+++ b/packages/language-server/src/lib/documents/parseHtml.ts
@@ -3,8 +3,11 @@ import {
     HTMLDocument,
     TokenType,
     ScannerState,
-    Scanner
+    Scanner,
+    Node,
+    Position
 } from 'vscode-html-languageservice';
+import { Document } from './Document';
 import { isInsideMoustacheTag } from './utils';
 
 const parser = getLanguageService();
@@ -83,3 +86,66 @@ function preprocess(text: string) {
         scanner = createScanner(text, offset, ScannerState.WithinTag);
     }
 }
+
+export interface AttributeContext {
+    name: string;
+    inValue: boolean;
+}
+
+export function getAttributeContextAtPosition(
+    document: Document,
+    position: Position
+): AttributeContext | null {
+    const offset = document.offsetAt(position);
+    const { html } = document;
+    const tag = html.findNodeAt(offset);
+
+    if (!inStartTag(offset, tag) || !tag.attributes) {
+        return null;
+    }
+
+    const text = document.getText();
+    const beforeStartTagEnd =
+        text.substring(0, tag.start) + preprocess(text.substring(tag.start, tag.startTagEnd));
+
+    const scanner = createScanner(beforeStartTagEnd, tag.start);
+
+    let token = scanner.scan();
+    let currentAttributeName: string | undefined;
+    const inTokenRange = () =>
+        scanner.getTokenOffset() <= offset && offset <= scanner.getTokenEnd();
+    while (token != TokenType.EOS) {
+        // adopted from https://github.com/microsoft/vscode-html-languageservice/blob/2f7ae4df298ac2c299a40e9024d118f4a9dc0c68/src/services/htmlCompletion.ts#L402
+        if (token === TokenType.AttributeName) {
+            currentAttributeName = scanner.getTokenText();
+            if (inTokenRange()) {
+                return {
+                    name: currentAttributeName,
+                    inValue: false
+                };
+            }
+        } else if (token === TokenType.DelimiterAssign) {
+            if (scanner.getTokenEnd() === offset && currentAttributeName) {
+                return {
+                    name: currentAttributeName,
+                    inValue: true
+                };
+            }
+        } else if (token === TokenType.AttributeValue) {
+            if (inTokenRange() && currentAttributeName) {
+                return {
+                    name: currentAttributeName,
+                    inValue: true
+                };
+            }
+            currentAttributeName = undefined;
+        }
+        token = scanner.scan();
+    }
+
+    return null;
+}
+
+function inStartTag(offset: number, node: Node) {
+    return offset > node.start && node.startTagEnd != undefined && offset < node.startTagEnd;
+}
diff --git a/packages/language-server/src/plugins/css/CSSPlugin.ts b/packages/language-server/src/plugins/css/CSSPlugin.ts
index 09f45266f..b1e3709a8 100644
--- a/packages/language-server/src/plugins/css/CSSPlugin.ts
+++ b/packages/language-server/src/plugins/css/CSSPlugin.ts
@@ -40,6 +40,8 @@ import {
 import { CSSDocument } from './CSSDocument';
 import { getLanguage, getLanguageService } from './service';
 import { GlobalVars } from './global-vars';
+import { getIdClassCompletion } from './features/getIdClassCompletion';
+import { getAttributeContextAtPosition } from '../../lib/documents/parseHtml';
 
 export class CSSPlugin
     implements
@@ -130,10 +132,10 @@ export class CSSPlugin
     ): CompletionList | null {
         const triggerCharacter = completionContext?.triggerCharacter;
         const triggerKind = completionContext?.triggerKind;
-        const isCustomTriggerCharater = triggerKind === CompletionTriggerKind.TriggerCharacter;
+        const isCustomTriggerCharacter = triggerKind === CompletionTriggerKind.TriggerCharacter;
 
         if (
-            isCustomTriggerCharater &&
+            isCustomTriggerCharacter &&
             triggerCharacter &&
             !this.triggerCharacters.includes(triggerCharacter)
         ) {
@@ -146,7 +148,11 @@ export class CSSPlugin
 
         const cssDocument = this.getCSSDoc(document);
         if (!cssDocument.isInGenerated(position)) {
-            return null;
+            const attributeContext = getAttributeContextAtPosition(document, position);
+            if (!attributeContext) {
+                return null;
+            }
+            return getIdClassCompletion(cssDocument, attributeContext) ?? null;
         }
 
         if (isSASS(cssDocument)) {
diff --git a/packages/language-server/src/plugins/css/features/getIdClassCompletion.ts b/packages/language-server/src/plugins/css/features/getIdClassCompletion.ts
new file mode 100644
index 000000000..c10877e67
--- /dev/null
+++ b/packages/language-server/src/plugins/css/features/getIdClassCompletion.ts
@@ -0,0 +1,69 @@
+import { CompletionItem, CompletionItemKind, CompletionList } from 'vscode-languageserver';
+import { AttributeContext } from '../../../lib/documents/parseHtml';
+import { CSSDocument } from '../CSSDocument';
+
+export function getIdClassCompletion(
+    cssDoc: CSSDocument,
+    attributeContext: AttributeContext
+): CompletionList | undefined {
+    const collectingType = getCollectingType(attributeContext);
+
+    if (!collectingType) {
+        return;
+    }
+    const items = collectSelectors(cssDoc.stylesheet as CSSNode, collectingType);
+
+    return CompletionList.create(items);
+}
+
+function getCollectingType(attributeContext: AttributeContext): number | undefined {
+    if (attributeContext.inValue) {
+        if (attributeContext.name === 'class') {
+            return NodeType.ClassSelector;
+        }
+        if (attributeContext.name === 'id') {
+            return NodeType.IdentifierSelector;
+        }
+    } else if (attributeContext.name.startsWith('class:')) {
+        return NodeType.ClassSelector;
+    }
+}
+
+/**
+ * incomplete see
+ * https://github.com/microsoft/vscode-css-languageservice/blob/master/src/parser/cssNodes.ts#L14
+ * The enum is not exported. we have to update this whenever it changes
+ */
+export enum NodeType {
+    ClassSelector = 14,
+    IdentifierSelector = 15
+}
+
+export type CSSNode = {
+    type: number;
+    children: CSSNode[] | undefined;
+    getText(): string;
+};
+
+export function collectSelectors(stylesheet: CSSNode, type: number) {
+    const result: CSSNode[] = [];
+    walk(stylesheet, (node) => {
+        if (node.type === type) {
+            result.push(node);
+        }
+    });
+
+    return result.map(
+        (node): CompletionItem => ({
+            label: node.getText().substring(1),
+            kind: CompletionItemKind.Keyword
+        })
+    );
+}
+
+function walk(node: CSSNode, callback: (node: CSSNode) => void) {
+    callback(node);
+    if (node.children) {
+        node.children.forEach((node) => walk(node, callback));
+    }
+}
diff --git a/packages/language-server/test/plugins/css/features/getIdClassCompletion.test.ts b/packages/language-server/test/plugins/css/features/getIdClassCompletion.test.ts
new file mode 100644
index 000000000..6d3321246
--- /dev/null
+++ b/packages/language-server/test/plugins/css/features/getIdClassCompletion.test.ts
@@ -0,0 +1,78 @@
+import assert from 'assert';
+import { CompletionItem, CompletionItemKind, CompletionList } from 'vscode-languageserver';
+import { Document, DocumentManager } from '../../../../src/lib/documents';
+import { LSConfigManager } from '../../../../src/ls-config';
+import { CSSPlugin } from '../../../../src/plugins';
+import { CSSDocument } from '../../../../src/plugins/css/CSSDocument';
+import {
+    collectSelectors,
+    NodeType,
+    CSSNode
+} from '../../../../src/plugins/css/features/getIdClassCompletion';
+
+describe('getIdClassCompletion', () => {
+    function createDocument(content: string) {
+        return new Document('file:///hello.svelte', content);
+    }
+
+    function createCSSDocument(content: string) {
+        return new CSSDocument(createDocument(content));
+    }
+
+    function testSelectors(items: CompletionItem[], expectedSelectors: string[]) {
+        assert.deepStrictEqual(
+            items.map((item) => item.label),
+            expectedSelectors,
+            'vscode-language-services might have changed the NodeType enum. Check if we need to update it'
+        );
+    }
+
+    it('collect css classes', () => {
+        const actual = collectSelectors(
+            createCSSDocument('<style>.abc {}</style>').stylesheet as CSSNode,
+            NodeType.ClassSelector
+        );
+        testSelectors(actual, ['abc']);
+    });
+
+    it('collect css ids', () => {
+        const actual = collectSelectors(
+            createCSSDocument('<style>#abc {}</style>').stylesheet as CSSNode,
+            NodeType.IdentifierSelector
+        );
+        testSelectors(actual, ['abc']);
+    });
+
+    function setup(content: string) {
+        const document = createDocument(content);
+        const docManager = new DocumentManager(() => document);
+        const pluginManager = new LSConfigManager();
+        const plugin = new CSSPlugin(docManager, pluginManager);
+        docManager.openDocument(<any>'some doc');
+        return { plugin, document };
+    }
+
+    it('provides css classes completion for class attribute', () => {
+        const { plugin, document } = setup('<div class=></div><style>.abc{}</style>');
+        assert.deepStrictEqual(plugin.getCompletions(document, { line: 0, character: 11 }), {
+            isIncomplete: false,
+            items: [{ label: 'abc', kind: CompletionItemKind.Keyword }]
+        } as CompletionList);
+    });
+
+    it('provides css classes completion for class directive', () => {
+        const { plugin, document } = setup('<div class:></div><style>.abc{}</style>');
+        assert.deepStrictEqual(plugin.getCompletions(document, { line: 0, character: 11 }), {
+            isIncomplete: false,
+            items: [{ label: 'abc', kind: CompletionItemKind.Keyword }]
+        } as CompletionList);
+    });
+
+    it('provides css id completion for id attribute', () => {
+        const { plugin, document } = setup('<div id=></div><style>#abc{}</style>');
+        assert.deepStrictEqual(plugin.getCompletions(document, { line: 0, character: 8 }), {
+            isIncomplete: false,
+            items: [{ label: 'abc', kind: CompletionItemKind.Keyword }]
+        } as CompletionList);
+    });
+});