diff --git a/packages/tailwindcss-language-service/src/util/color.ts b/packages/tailwindcss-language-service/src/util/color.ts
index 2adb5c84..3c59f437 100644
--- a/packages/tailwindcss-language-service/src/util/color.ts
+++ b/packages/tailwindcss-language-service/src/util/color.ts
@@ -56,7 +56,7 @@ const colorRegex = new RegExp(
   'gi',
 )
 
-function getColorsInString(str: string): (culori.Color | KeywordColor)[] {
+function getColorsInString(state: State, str: string): (culori.Color | KeywordColor)[] {
   if (/(?:box|drop)-shadow/.test(str)) return []
 
   function toColor(match: RegExpMatchArray) {
@@ -64,7 +64,7 @@ function getColorsInString(str: string): (culori.Color | KeywordColor)[] {
     return getKeywordColor(color) ?? culori.parse(color)
   }
 
-  str = replaceCssVarsWithFallbacks(str)
+  str = replaceCssVarsWithFallbacks(state, str)
   str = removeColorMixWherePossible(str)
 
   let possibleColors = str.matchAll(colorRegex)
@@ -73,6 +73,7 @@ function getColorsInString(str: string): (culori.Color | KeywordColor)[] {
 }
 
 function getColorFromDecls(
+  state: State,
   decls: Record<string, string | string[]>,
 ): culori.Color | KeywordColor | null {
   let props = Object.keys(decls).filter((prop) => {
@@ -99,7 +100,9 @@ function getColorFromDecls(
 
   const propsToCheck = areAllCustom ? props : nonCustomProps
 
-  const colors = propsToCheck.flatMap((prop) => ensureArray(decls[prop]).flatMap(getColorsInString))
+  const colors = propsToCheck.flatMap((prop) => ensureArray(decls[prop]).flatMap((str) => {
+    return getColorsInString(state, str)
+  }))
 
   // check that all of the values are valid colors
   // if (colors.some((color) => color instanceof TinyColor && !color.isValid)) {
@@ -170,7 +173,7 @@ function getColorFromRoot(state: State, css: postcss.Root): culori.Color | Keywo
     decls[decl.prop].push(decl.value)
   })
 
-  return getColorFromDecls(decls)
+  return getColorFromDecls(state, decls)
 }
 
 export function getColor(state: State, className: string): culori.Color | KeywordColor | null {
@@ -186,7 +189,7 @@ export function getColor(state: State, className: string): culori.Color | Keywor
     if (state.classNames) {
       const item = dlv(state.classNames.classNames, [className, '__info'])
       if (item && item.__rule) {
-        return getColorFromDecls(removeMeta(item))
+        return getColorFromDecls(state, removeMeta(item))
       }
     }
 
@@ -215,7 +218,7 @@ export function getColor(state: State, className: string): culori.Color | Keywor
         decls[decl.prop] = decl.value
       }
     })
-    return getColorFromDecls(decls)
+    return getColorFromDecls(state, decls)
   }
 
   let parts = getClassNameParts(state, className)
@@ -224,7 +227,7 @@ export function getColor(state: State, className: string): culori.Color | Keywor
   const item = dlv(state.classNames.classNames, [...parts, '__info'])
   if (!item.__rule) return null
 
-  return getColorFromDecls(removeMeta(item))
+  return getColorFromDecls(state, removeMeta(item))
 }
 
 export function getColorFromValue(value: unknown): culori.Color | KeywordColor | null {
diff --git a/packages/tailwindcss-language-service/src/util/css-vars.test.ts b/packages/tailwindcss-language-service/src/util/css-vars.test.ts
index e1a85078..3b531fd4 100644
--- a/packages/tailwindcss-language-service/src/util/css-vars.test.ts
+++ b/packages/tailwindcss-language-service/src/util/css-vars.test.ts
@@ -1,26 +1,56 @@
 import { expect, test } from 'vitest'
 import { replaceCssVarsWithFallbacks } from './css-vars'
+import { State } from './state'
+import { DesignSystem } from './v4'
 
 test('replacing CSS variables with their fallbacks (when they have them)', () => {
-  expect(replaceCssVarsWithFallbacks('var(--foo, red)')).toBe(' red')
-  expect(replaceCssVarsWithFallbacks('var(--foo, )')).toBe(' ')
+  let map = new Map<string, string>([
+      ['--known', 'blue'],
+  ])
 
-  expect(replaceCssVarsWithFallbacks('rgb(var(--foo, 255 0 0))')).toBe('rgb( 255 0 0)')
-  expect(replaceCssVarsWithFallbacks('rgb(var(--foo, var(--bar)))')).toBe('rgb( var(--bar))')
+  let state: State = {
+    enabled: true,
+    designSystem: {
+      resolveThemeValue: (name) => map.get(name) ?? null,
+    } as DesignSystem,
+  }
+
+  expect(replaceCssVarsWithFallbacks(state, 'var(--foo, red)')).toBe(' red')
+  expect(replaceCssVarsWithFallbacks(state, 'var(--foo, )')).toBe(' ')
+
+  expect(replaceCssVarsWithFallbacks(state, 'rgb(var(--foo, 255 0 0))')).toBe('rgb( 255 0 0)')
+  expect(replaceCssVarsWithFallbacks(state, 'rgb(var(--foo, var(--bar)))')).toBe('rgb( var(--bar))')
 
   expect(
-    replaceCssVarsWithFallbacks('rgb(var(var(--bar, var(--baz), var(--qux), var(--thing))))'),
+    replaceCssVarsWithFallbacks(
+      state,
+      'rgb(var(var(--bar, var(--baz), var(--qux), var(--thing))))',
+    ),
   ).toBe('rgb(var(var(--bar, var(--baz), var(--qux), var(--thing))))')
 
   expect(
     replaceCssVarsWithFallbacks(
+      state,
       'rgb(var(--one, var(--bar, var(--baz), var(--qux), var(--thing))))',
     ),
   ).toBe('rgb(  var(--baz), var(--qux), var(--thing))')
 
   expect(
     replaceCssVarsWithFallbacks(
+      state,
       'color-mix(in srgb, var(--color-primary, oklch(0 0 0 / 2.5)), var(--color-secondary, oklch(0 0 0 / 2.5)), 50%)',
     ),
   ).toBe('color-mix(in srgb,  oklch(0 0 0 / 2.5),  oklch(0 0 0 / 2.5), 50%)')
+
+  // Known theme keys are replaced with their values
+  expect(replaceCssVarsWithFallbacks(state, 'var(--known)')).toBe('blue')
+
+  // Values from the theme take precedence over fallbacks
+  expect(replaceCssVarsWithFallbacks(state, 'var(--known, red)')).toBe('blue')
+
+  // Unknown theme keys use a fallback if provided
+  expect(replaceCssVarsWithFallbacks(state, 'var(--unknown, red)')).toBe(' red')
+
+  // Unknown theme keys without fallbacks are not replaced
+  expect(replaceCssVarsWithFallbacks(state, 'var(--unknown)')).toBe('var(--unknown)')
 })
diff --git a/packages/tailwindcss-language-service/src/util/css-vars.ts b/packages/tailwindcss-language-service/src/util/css-vars.ts
index ec6803dd..032153fe 100644
--- a/packages/tailwindcss-language-service/src/util/css-vars.ts
+++ b/packages/tailwindcss-language-service/src/util/css-vars.ts
@@ -1,4 +1,27 @@
-export function replaceCssVarsWithFallbacks(str: string): string {
+import type { State } from './state'
+
+export function replaceCssVarsWithFallbacks(state: State, str: string): string {
+  return replaceCssVars(str, (name, fallback) => {
+    // Replace with the value from the design system first. The design system
+    // take precedences over other sources as that emulates the behavior of a
+    // browser where the fallback is only used if the variable is defined.
+    if (state.designSystem && name.startsWith('--')) {
+      let value = state.designSystem.resolveThemeValue?.(name) ?? null
+      if (value !== null) return value
+    }
+
+    if (fallback) {
+      return fallback
+    }
+
+    // Don't touch it since there's no suitable replacement
+    return null
+  })
+}
+
+type CssVarReplacer = (name: string, fallback: string | null) => string | null
+
+function replaceCssVars(str: string, replace: CssVarReplacer): string {
   for (let i = 0; i < str.length; ++i) {
     if (!str.startsWith('var(', i)) continue
 
@@ -13,13 +36,31 @@ export function replaceCssVarsWithFallbacks(str: string): string {
       } else if (str[j] === ',' && depth === 0 && fallbackStart === null) {
         fallbackStart = j + 1
       } else if (str[j] === ')' && depth === 0) {
+        let varName: string
+        let fallback: string | null
+
         if (fallbackStart === null) {
-          i = j + 1
+          varName = str.slice(i + 4, j)
+          fallback = null
+        } else {
+          varName = str.slice(i + 4, fallbackStart - 1)
+          fallback = str.slice(fallbackStart, j)
+        }
+
+        let replacement = replace(varName, fallback)
+
+        if (replacement !== null) {
+          str = str.slice(0, i) + replacement + str.slice(j + 1)
+
+          // We don't want to skip past anything here because `replacement`
+          // might contain more var(…) calls in which case `i` will already
+          // be pointing at the right spot to start looking for them
           break
         }
 
-        let fallbackEnd = j
-        str = str.slice(0, i) + str.slice(fallbackStart, fallbackEnd) + str.slice(j + 1)
+        // It can't be replaced so we can avoid unncessary work by skipping over
+        // the entire var(…) call.
+        i = j + 1
         break
       }
     }
diff --git a/packages/tailwindcss-language-service/src/util/v4/design-system.ts b/packages/tailwindcss-language-service/src/util/v4/design-system.ts
index 75da6316..ca2f9ad2 100644
--- a/packages/tailwindcss-language-service/src/util/v4/design-system.ts
+++ b/packages/tailwindcss-language-service/src/util/v4/design-system.ts
@@ -37,4 +37,7 @@ export interface DesignSystem {
 export interface DesignSystem {
   compile(classes: string[]): postcss.Root[]
   toCss(nodes: postcss.Root | postcss.Node[]): string
+
+  // Optional because it did not exist in earlier v4 alpha versions
+  resolveThemeValue?(path: string): string | undefined
 }
diff --git a/packages/vscode-tailwindcss/CHANGELOG.md b/packages/vscode-tailwindcss/CHANGELOG.md
index 612a7268..dd0acd52 100644
--- a/packages/vscode-tailwindcss/CHANGELOG.md
+++ b/packages/vscode-tailwindcss/CHANGELOG.md
@@ -7,6 +7,7 @@
 - Support loading TypeScript configs and plugins in v4 projects ([#1076](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1076))
 - Show colors for logical border properties ([#1075](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1075))
 - Show all potential class conflicts in v4 projects ([#1077](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1077))
+- Lookup variables in the CSS theme ([#1082](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1082))
 
 ## 0.12.12