diff --git a/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikit.module b/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikit.module
index 906a00b5..5554c9d6 100644
--- a/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikit.module
+++ b/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikit.module
@@ -20,7 +20,8 @@
  * @property string $inputSize Size for input/select elements. One of "s" for small, "m" for medium (default), or "l" for large. 
  * @property bool|int $ukGrid When true, use uk-width classes for Inputfields (rather than CSS percentages). 
  * @property int $toggleBehavior (0=Standard, 1=Consistent)
- * property string $configPhpHash Hash used internally to detect changes to $config->AdminThemeUikit settings.
+ * @property string $configPhpHash Hash used internally to detect changes to $config->AdminThemeUikit settings.
+ * @property int $cssVersion Current version number of core CSS/LESS files
  * 
  * @method string getUikitCSS()
  * 
@@ -31,7 +32,7 @@ class AdminThemeUikit extends AdminThemeFramework implements Module, Configurabl
 	public static function getModuleInfo() {
 		return array(
 			'title' => 'Uikit',
-			'version' => 32,
+			'version' => 33,
 			'summary' => 'Uikit v3 admin theme',
 			'autoload' => 'template=admin', 
 		); 
@@ -51,6 +52,14 @@ class AdminThemeUikit extends AdminThemeFramework implements Module, Configurabl
 	 */
 	const upgrade = false;
 
+	/**
+	 * Required CSS/LESS files version 
+	 * 
+	 * Increment on core less file changes that will also require a recompile of /site/assets/admin.css
+	 * 
+	 */
+	const requireCssVersion = 1;
+
 	/**
 	 * Default logo image file (relative to this dir)
 	 * 
@@ -93,6 +102,7 @@ class AdminThemeUikit extends AdminThemeFramework implements Module, Configurabl
 		$this->set('inputSize', 'm'); // m=medium (default), s=small, l=large
 		$this->set('ukGrid', false); 
 		$this->set('configPhpHash', '');
+		$this->set('cssVersion', 0);
 		$this->setClasses(array(
 			'input' => 'uk-input',
 			'input-small' => 'uk-input uk-form-small',
@@ -1092,6 +1102,7 @@ class AdminThemeUikit extends AdminThemeFramework implements Module, Configurabl
 		
 		$settings = $config->AdminThemeUikit; 
 		if(!is_array($settings)) $settings = array();
+		$settings['requireCssVersion'] = self::requireCssVersion;
 		
 		if(self::upgrade) {
 			$settings['upgrade'] = true;
diff --git a/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikitCss.php b/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikitCss.php
index 0cfeb53f..71068db5 100644
--- a/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikitCss.php
+++ b/wire/modules/AdminTheme/AdminThemeUikit/AdminThemeUikitCss.php
@@ -15,6 +15,8 @@
  * 
  * @property string $configPhpHash Hash used internally to detect changes to $config->AdminThemeUikit settings.
  * @property string $configPhpName Name of property in $config that holds custom settings (default='AdminThemeUikit').
+ * @property int $requireCssVersion
+ * @property int $cssVersion
  *
  * Settings that may be specified in $config->AdminThemeUikit array:
  * 
@@ -30,11 +32,11 @@
 class AdminThemeUikitCss extends WireData {
 
 	/**
-	 * @var AdminTheme
+	 * @var AdminTheme|AdminThemeUikit
 	 * 
 	 */
 	protected $adminTheme;
-
+	
 	/**
 	 * Construct
 	 * 
@@ -68,6 +70,8 @@ class AdminThemeUikitCss extends WireData {
 			'configPhpName' => $this->adminTheme->className(),
 			'configPhpHash' => $this->adminTheme->get('configPhpHash'),
 			'replacements' => array(),
+			'cssVersion' => (int) $this->adminTheme->get('cssVersion'),
+			'requireCssVersion' => 0,
 		);
 	}
 	
@@ -101,12 +105,16 @@ class AdminThemeUikitCss extends WireData {
 				if($mtime > $lessTime) $lessTime = $mtime;
 			}
 			
-			if(!count($lessFiles)) return $this->getDefaultCssFile($getPath);
+			if(!count($lessFiles) && ($this->style === '' || $this->style === $this->defaultStyle)) {
+				return $this->getDefaultCssFile($getPath);
+			}
 
 			$cssFile = $this->customFile($this->customCssFile, 'css');
-			if(!$cssFile) return $this->getDefaultCssFile();
+			if(!$cssFile) return $this->getDefaultCssFile($getPath);
+			
 			$cssTime = is_file($cssFile) ? (int) filemtime($cssFile) : 0;
-			$recompile = $this->recompile || $lessTime > $cssTime || $this->configPhpSettingsChanged();
+			$recompile = $this->recompile || $lessTime > $cssTime || $this->cssVersion < $this->requireCssVersion; 
+			if(!$recompile && $this->configPhpSettingsChanged()) $recompile = true;
 		}
 
 		if($recompile) try {
@@ -117,8 +125,14 @@ class AdminThemeUikitCss extends WireData {
 			$less->addFiles($lessFiles);
 			$options = array('replacements' => $this->replacements); 
 			if(!$less->saveCss($cssFile, $options)) throw new WireException("Compile error: $cssFile");
-			$this->message(sprintf($this->_('Compiled: %s'), $cssFile), Notice::noGroup);
+			$messages = array(sprintf($this->_('Compiled: %s'), $cssFile));
 			$cssTime = filemtime($cssFile);
+			if($this->cssVersion < $this->requireCssVersion) {
+				$messages[] = "(core CSS v$this->cssVersion => v$this->requireCssVersion)";
+				$modules->saveConfig($this->adminTheme, 'cssVersion', $this->requireCssVersion);
+				$this->adminTheme->set('cssVersion', $this->requireCssVersion);
+			}
+			$this->message(implode(' ', $messages), Notice::noGroup);
 		} catch(\Exception $e) {
 			$this->error('LESS - ' . $e->getMessage(), Notice::noGroup);
 		}
diff --git a/wire/modules/AdminTheme/AdminThemeUikit/install-foot.inc b/wire/modules/AdminTheme/AdminThemeUikit/install-foot.inc
index 4a4a50f2..5d0f37bc 100644
--- a/wire/modules/AdminTheme/AdminThemeUikit/install-foot.inc
+++ b/wire/modules/AdminTheme/AdminThemeUikit/install-foot.inc
@@ -10,7 +10,7 @@ if(!defined("PROCESSWIRE_INSTALL")) die();
 	<!-- FOOTER -->
 	<footer id='pw-footer' class='uk-margin'>
 		<div class='pw-container uk-container uk-container-center'>
-			<p>ProcessWire 3.x &copy; 2020</p>
+			<p>ProcessWire 3.x &copy; 2021</p>
 		</div>
 	</footer>
 
@@ -19,4 +19,4 @@ if(!defined("PROCESSWIRE_INSTALL")) die();
 	</script>
 
 </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/wire/modules/AdminTheme/AdminThemeUikit/interfaces.php b/wire/modules/AdminTheme/AdminThemeUikit/interfaces.php
index fed1ad61..dfbe2424 100644
--- a/wire/modules/AdminTheme/AdminThemeUikit/interfaces.php
+++ b/wire/modules/AdminTheme/AdminThemeUikit/interfaces.php
@@ -23,10 +23,11 @@ interface AdminThemeUikitLessInterface {
 
 	/**
 	 * @param string $file
+	 * @param string $url
 	 * @return self
 	 *
 	 */
-	public function addFile($file);
+	public function addFile($file, $url = '');
 
 	/**
 	 * @param array $files
@@ -37,10 +38,11 @@ interface AdminThemeUikitLessInterface {
 
 	/**
 	 * @param string $file
+	 * @param array $options
 	 * @return bool
 	 *
 	 */
-	public function saveCss($file);
+	public function saveCss($file, array $options = array());
 
 	/**
 	 * @return string