diff --git a/lib/private/Template/SCSSCacher.php b/lib/private/Template/SCSSCacher.php
index c6473ead09..8830a651f3 100644
--- a/lib/private/Template/SCSSCacher.php
+++ b/lib/private/Template/SCSSCacher.php
@@ -57,6 +57,9 @@ class SCSSCacher {
 	/** @var IConfig */
 	protected $config;
 
+	/** @var \OC_Defaults */
+	private $defaults;
+
 	/** @var string */
 	protected $serverRoot;
 
@@ -64,7 +67,7 @@ class SCSSCacher {
 	protected $depsCache;
 
 	/** @var null|string */
-	protected $injectedVariables = null;
+	private $injectedVariables;
 
 	/**
 	 * @param ILogger $logger
@@ -93,12 +96,14 @@ class SCSSCacher {
 
 	/**
 	 * Process the caching process if needed
+	 *
 	 * @param string $root Root path to the nextcloud installation
 	 * @param string $file
 	 * @param string $app The app name
 	 * @return boolean
+	 * @throws NotPermittedException
 	 */
-	public function process($root, $file, $app) {
+	public function process(string $root, string $file, string $app): bool {
 		$path = explode('/', $root . '/' . $file);
 
 		$fileNameSCSS = array_pop($path);
@@ -126,7 +131,7 @@ class SCSSCacher {
 	 * @param $fileName
 	 * @return ISimpleFile
 	 */
-	public function getCachedCSS($appName, $fileName) {
+	public function getCachedCSS(string $appName, string $fileName): ISimpleFile {
 		$folder = $this->appData->getFolder($appName);
 		return $folder->getFile($this->prependBaseurlPrefix($fileName));
 	}
@@ -137,7 +142,7 @@ class SCSSCacher {
 	 * @param ISimpleFolder $folder
 	 * @return boolean
 	 */
-	private function isCached($fileNameCSS, ISimpleFolder $folder) {
+	private function isCached(string $fileNameCSS, ISimpleFolder $folder) {
 		try {
 			$cachedFile = $folder->getFile($fileNameCSS);
 			if ($cachedFile->getSize() > 0) {
@@ -151,7 +156,7 @@ class SCSSCacher {
 				}
 				$deps = json_decode($deps, true);
 
-				foreach ($deps as $file=>$mtime) {
+				foreach ((array)$deps as $file=>$mtime) {
 					if (!file_exists($file) || filemtime($file) > $mtime) {
 						return false;
 					}
@@ -168,7 +173,7 @@ class SCSSCacher {
 	 * Check if the variables file has changed
 	 * @return bool
 	 */
-	private function variablesChanged() {
+	private function variablesChanged(): bool {
 		$injectedVariables = $this->getInjectedVariables();
 		if($this->config->getAppValue('core', 'scss.variables') !== md5($injectedVariables)) {
 			$this->resetCache();
@@ -180,14 +185,16 @@ class SCSSCacher {
 
 	/**
 	 * Cache the file with AppData
+	 *
 	 * @param string $path
 	 * @param string $fileNameCSS
 	 * @param string $fileNameSCSS
 	 * @param ISimpleFolder $folder
 	 * @param string $webDir
 	 * @return boolean
+	 * @throws NotPermittedException
 	 */
-	private function cache($path, $fileNameCSS, $fileNameSCSS, ISimpleFolder $folder, $webDir) {
+	private function cache(string $path, string $fileNameCSS, string $fileNameSCSS, ISimpleFolder $folder, string $webDir) {
 		$scss = new Compiler();
 		$scss->setImportPaths([
 			$path,
@@ -261,7 +268,7 @@ class SCSSCacher {
 		}
 		foreach ($appDirectory as $folder) {
 			foreach ($folder->getDirectoryListing() as $file) {
-				if (substr($file->getName(), -3) === "css" || substr($file->getName(), -4) === "deps") {
+				if (substr($file->getName(), -3) === 'css' || substr($file->getName(), -4) === 'deps') {
 					$file->delete();
 				}
 			}
@@ -271,9 +278,10 @@ class SCSSCacher {
 	/**
 	 * @return string SCSS code for variables from OC_Defaults
 	 */
-	private function getInjectedVariables() {
-		if ($this->injectedVariables !== null)
+	private function getInjectedVariables(): string {
+		if ($this->injectedVariables !== null) {
 			return $this->injectedVariables;
+		}
 		$variables = '';
 		foreach ($this->defaults->getScssVariables() as $key => $value) {
 			$variables .= '$' . $key . ': ' . $value . ';';
@@ -297,7 +305,7 @@ class SCSSCacher {
 	 * @param string $webDir
 	 * @return string
 	 */
-	private function rebaseUrls($css, $webDir) {
+	private function rebaseUrls(string $css, string $webDir): string {
 		$re = '/url\([\'"]([^\/][\.\w?=\/-]*)[\'"]\)/x';
 		$subst = 'url(\''.$webDir.'/$1\')';
 		return preg_replace($re, $subst, $css);
@@ -309,20 +317,20 @@ class SCSSCacher {
 	 * @param string $fileName
 	 * @return string
 	 */
-	public function getCachedSCSS($appName, $fileName) {
+	public function getCachedSCSS(string $appName, string $fileName): string {
 		$tmpfileLoc = explode('/', $fileName);
 		$fileName = array_pop($tmpfileLoc);
 		$fileName = $this->prependBaseurlPrefix(str_replace('.scss', '.css', $fileName));
 
-		return substr($this->urlGenerator->linkToRoute('core.Css.getCss', array('fileName' => $fileName, 'appName' => $appName)), strlen(\OC::$WEBROOT) + 1);
+		return substr($this->urlGenerator->linkToRoute('core.Css.getCss', ['fileName' => $fileName, 'appName' => $appName]), strlen(\OC::$WEBROOT) + 1);
 	}
 
 	/**
 	 * Prepend hashed base url to the css file
-	 * @param $cssFile
+	 * @param string$cssFile
 	 * @return string
 	 */
-	private function prependBaseurlPrefix($cssFile) {
+	private function prependBaseurlPrefix(string $cssFile): string {
 		$frontendController = ($this->config->getSystemValue('htaccess.IgnoreFrontController', false) === true || getenv('front_controller_active') === 'true');
 		return substr(md5($this->urlGenerator->getBaseUrl() . $frontendController), 0, 8) . '-' . $cssFile;
 	}
@@ -335,7 +343,7 @@ class SCSSCacher {
 	 * @param string $webRoot the nextcloud installation root path
 	 * @return string the webDir
 	 */
-	private function getWebDir($path, $appName, $serverRoot, $webRoot) {
+	private function getWebDir(string $path, string $appName, string $serverRoot, string $webRoot): string {
 		// Detect if path is within server root AND if path is within an app path
 		if ( strpos($path, $serverRoot) === false && $appWebPath = \OC_App::getAppWebPath($appName)) {
 			// Get the file path within the app directory