diff --git a/src/lsp/providers/diagnosticsProvider.ts b/src/lsp/providers/diagnosticsProvider.ts
index e76bf49249f86a753313ebc8aecd65c29403d89a..9f483ac9f69be7fbc5deeae70607194fafacf66b 100644
--- a/src/lsp/providers/diagnosticsProvider.ts
+++ b/src/lsp/providers/diagnosticsProvider.ts
@@ -5,10 +5,18 @@   DiagnosticSeverity,
 } from 'vscode-languageserver'
 import { State } from '../util/state'
 import { isCssDoc } from '../util/css'
+import {
+  findClassNamesInRange,
+  findClassListsInDocument,
+  getClassNamesInClassList,
+} from '../util/find'
+import { getClassNameMeta } from '../util/getClassNameMeta'
+import { State } from '../util/state'
 import { findClassNamesInRange } from '../util/find'
+import { State } from '../util/state'
 import { getClassNameMeta } from '../util/getClassNameMeta'
 
-function provideCssDiagnostics(state: State, document: TextDocument): void {
+function getCssDiagnostics(state: State, document: TextDocument): Diagnostic[] {
   const classNames = findClassNamesInRange(document, undefined, 'css')
 
   let diagnostics: Diagnostic[] = classNames
@@ -46,57 +54,96 @@       return {
         severity: DiagnosticSeverity.Error,
         range,
         message,
-        // source: 'ex',
       }
     })
     .filter(Boolean)
 
-  DiagnosticSeverity,
+  return diagnostics
+}
+
+function getConflictDiagnostics(
+  state: State,
+  document: TextDocument
+): Diagnostic[] {
+import { isCssDoc } from '../util/css'
   DiagnosticSeverity,
-  DiagnosticSeverity,
+import { isCssDoc } from '../util/css'
 } from 'vscode-languageserver'
-  DiagnosticSeverity,
+
+import { isCssDoc } from '../util/css'
 import { State } from '../util/state'
-  DiagnosticSeverity,
+import { isCssDoc } from '../util/css'
 import { isCssDoc } from '../util/css'
-  DiagnosticSeverity,
+
+import { isCssDoc } from '../util/css'
 import { findClassNamesInRange } from '../util/find'
-  DiagnosticSeverity,
+import { isCssDoc } from '../util/css'
 import { getClassNameMeta } from '../util/getClassNameMeta'
-} from 'vscode-languageserver'
+import { findClassNamesInRange } from '../util/find'
-} from 'vscode-languageserver'
+import { findClassNamesInRange } from '../util/find'
 import {
-} from 'vscode-languageserver'
+import { findClassNamesInRange } from '../util/find'
   TextDocument,
+
+        let otherDecls = getClassNameDecls(state, otherClassName.className)
+import { findClassNamesInRange } from '../util/find'
   DiagnosticSeverity,
+
+        let meta = getClassNameMeta(state, className.className)
+import { findClassNamesInRange } from '../util/find'
 import { State } from '../util/state'
-  DiagnosticSeverity,
+
+import { findClassNamesInRange } from '../util/find'
 import { isCssDoc } from '../util/css'
-  DiagnosticSeverity,
+import { findClassNamesInRange } from '../util/find'
 import { findClassNamesInRange } from '../util/find'
-  DiagnosticSeverity,
+import { findClassNamesInRange } from '../util/find'
 import { getClassNameMeta } from '../util/getClassNameMeta'
-} from 'vscode-languageserver'
+import { getClassNameMeta } from '../util/getClassNameMeta'
-} from 'vscode-languageserver'
+import { getClassNameMeta } from '../util/getClassNameMeta'
 import {
-} from 'vscode-languageserver'
+import { getClassNameMeta } from '../util/getClassNameMeta'
   TextDocument,
+        ) {
+          diagnostics.push({
+import { getClassNameMeta } from '../util/getClassNameMeta'
 } from 'vscode-languageserver'
+            severity: DiagnosticSeverity.Warning,
+            message: `You can’t use \`${className.className}\` and \`${otherClassName.className}\` together`,
+            relatedInformation: [
+              {
+                message: otherClassName.className,
+                location: {
+                  uri: document.uri,
+
   Diagnostic,
+                },
+
 } from 'vscode-languageserver'
+            ],
+          })
+        }
+      })
   DiagnosticSeverity,
+  TextDocument,
 
+import { getClassNameMeta } from '../util/getClassNameMeta'
-  state.editor.connection.sendDiagnostics({ uri: document.uri, diagnostics })
+
+  return diagnostics
 }
 
 export async function provideDiagnostics(
   state: State,
   document: TextDocument
 ): Promise<void> {
-import { State } from '../util/state'
+  state.editor.connection.sendDiagnostics({
+function provideCssDiagnostics(state: State, document: TextDocument): void {
 import {
-import { State } from '../util/state'
+function provideCssDiagnostics(state: State, document: TextDocument): void {
   TextDocument,
-import { State } from '../util/state'
+function provideCssDiagnostics(state: State, document: TextDocument): void {
   Diagnostic,
+      ...(isCssDoc(state, document) ? getCssDiagnostics(state, document) : []),
+    ],
+  })
 }

diff --git a/src/lsp/util/find.ts b/src/lsp/util/find.ts
index 6b1bfca7fbce3737b86c7529b4e7141715d17f58..9a04ac4de58771e60379719acd0b50a5e1ebcdf2 100644
--- a/src/lsp/util/find.ts
+++ b/src/lsp/util/find.ts
@@ -6,6 +6,7 @@ import { isHtmlContext, isHtmlDoc, isSvelteDoc, isVueDoc } from './html'
 import { isWithinRange } from './isWithinRange'
 import { isJsContext, isJsDoc } from './js'
 import { getClassAttributeLexer } from './lexers'
+import { flatten } from '../../util/array'
 
 export function findAll(re: RegExp, str: string): RegExpMatchArray[] {
   let match: RegExpMatchArray
@@ -25,57 +26,89 @@   return matches[matches.length - 1]
 }
 
 import { DocumentClassName, DocumentClassList, State } from './state'
+}
+  classList,
+  range,
+}: DocumentClassList): DocumentClassName[] {
+  const parts = classList.split(/(\s+)/)
+  const names: DocumentClassName[] = []
+  return matches[matches.length - 1]
 import lineColumn from 'line-column'
+import { DocumentClassName, DocumentClassList, State } from './state'
   doc: TextDocument,
 import { DocumentClassName, DocumentClassList, State } from './state'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isHtmlContext, isHtmlDoc, isSvelteDoc, isVueDoc } from './html'
+import { DocumentClassName, DocumentClassList, State } from './state'
   mode?: 'html' | 'css'
 import { DocumentClassName, DocumentClassList, State } from './state'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isJsContext, isJsDoc } from './js'
+import { DocumentClassName, DocumentClassList, State } from './state'
   const classLists = findClassListsInRange(doc, range, mode)
 import { DocumentClassName, DocumentClassList, State } from './state'
+import { DocumentClassName, DocumentClassList, State } from './state'
 
+import { DocumentClassName, DocumentClassList, State } from './state'
     [],
+import { DocumentClassName, DocumentClassList, State } from './state'
     classLists.map(({ classList, range }) => {
+import { DocumentClassName, DocumentClassList, State } from './state'
       const parts = classList.split(/(\s+)/)
+import { DocumentClassName, DocumentClassList, State } from './state'
       const names: DocumentClassName[] = []
+import { DocumentClassName, DocumentClassList, State } from './state'
       let index = 0
+import { DocumentClassName, DocumentClassList, State } from './state'
       for (let i = 0; i < parts.length; i++) {
+import { DocumentClassName, DocumentClassList, State } from './state'
         if (i % 2 === 0) {
+import { DocumentClassName, DocumentClassList, State } from './state'
           const start = indexToPosition(classList, index)
+            character:
+import { DocumentClassName, DocumentClassList, State } from './state'
           const end = indexToPosition(classList, index + parts[i].length)
+          },
+        },
+      })
+    }
+import { DocumentClassName, DocumentClassList, State } from './state'
           names.push({
+  }
+import { DocumentClassName, DocumentClassList, State } from './state'
             className: parts[i],
-import { isCssContext, isCssDoc } from './css'
 import { TextDocument, Range, Position } from 'vscode-languageserver'
+import { isJsContext, isJsDoc } from './js'
-              start: {
+
-import { isCssContext, isCssDoc } from './css'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import lineColumn from 'line-column'
-import { isCssContext, isCssDoc } from './css'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isCssContext, isCssDoc } from './css'
-import { isCssContext, isCssDoc } from './css'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isHtmlContext, isHtmlDoc, isSvelteDoc, isVueDoc } from './html'
-import { isCssContext, isCssDoc } from './css'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isWithinRange } from './isWithinRange'
-import { isCssContext, isCssDoc } from './css'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isJsContext, isJsDoc } from './js'
-import { isCssContext, isCssDoc } from './css'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { getClassAttributeLexer } from './lexers'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isCssContext, isCssDoc } from './css'
-
+import { TextDocument, Range, Position } from 'vscode-languageserver'
-                character:
+}
-                  (end.line === 0 ? range.start.character : 0) + end.character,
+
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isCssContext, isCssDoc } from './css'
-import { isJsContext, isJsDoc } from './js'
+import { DocumentClassName, DocumentClassList, State } from './state'
+import { TextDocument, Range, Position } from 'vscode-languageserver'
             },
+import { TextDocument, Range, Position } from 'vscode-languageserver'
           })
-        }
+): DocumentClassName[] {
-import { isHtmlContext, isHtmlDoc, isSvelteDoc, isVueDoc } from './html'
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isCssContext, isCssDoc } from './css'
-      }
-      return names
-    })
+import lineColumn from 'line-column'
-  )
+  return flatten(classLists.map(getClassNamesInClassList))
 }
 
 export function findClassListsInCssRange(
@@ -112,8 +145,7 @@ }
 
 export function findClassListsInHtmlRange(
   doc: TextDocument,
-import { getClassAttributeLexer } from './lexers'
 import { isWithinRange } from './isWithinRange'
 ): DocumentClassList[] {
   const text = doc.getText(range)
   const matches = findAll(/[\s:]class(?:Name)?=['"`{]/g, text)
@@ -189,17 +220,21 @@           return {
             classList: value,
             range: {
               start: {
+  doc: TextDocument,
 import { isCssContext, isCssDoc } from './css'
-import lineColumn from 'line-column'
                 character:
+import { DocumentClassName, DocumentClassList, State } from './state'
                   (end.line === 0 ? range.start.character : 0) +
                   start.character,
               },
               end: {
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isCssContext, isCssDoc } from './css'
-
+import { isWithinRange } from './isWithinRange'
                 character:
+  doc: TextDocument,
 import { isHtmlContext, isHtmlDoc, isSvelteDoc, isVueDoc } from './html'
+                  end.character,
               },
             },
           }
@@ -212,9 +248,9 @@ }
 
 export function findClassListsInRange(
   doc: TextDocument,
-    matches.push({ ...match })
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isHtmlContext, isHtmlDoc, isSvelteDoc, isVueDoc } from './html'
-    matches.push({ ...match })
+import { DocumentClassName, DocumentClassList, State } from './state'
 import { isWithinRange } from './isWithinRange'
 ): DocumentClassList[] {
   if (mode === 'css') {