use workdir for build

Dockerfile

 # Bootstrap SCSS
 FROM node:lts-alpine AS buildJS
 WORKDIR /build
-COPY . /build
-RUN mkdir /build/public/js
-RUN mkdir /build/public/css
+COPY . .
+RUN mkdir public/js
+RUN mkdir public/css
 RUN yarn install
 RUN yarn compile
 
 # Install PHP dependencies
 FROM composer:2 AS composer
 WORKDIR /build
-COPY --from=buildJS /build /build
-RUN cd /build/public/API && composer install
+COPY --from=buildJS . .
+RUN cd public/API && composer install
 
 # Prepare Webserver
 FROM gitlab.jonasled.de/jonasled/apache-php-minimal:latest
@@ -25,4 +25,4 @@ RUN apk update && \
 # |--------------------------------------------------------------------------
 # | copy website from node build
 # |--------------------------------------------------------------------------
-COPY --from=composer /build/public /var/www/localhost/htdocs/
\ No newline at end of file
+COPY --from=composer public .
\ No newline at end of file