I created a custom Theme with "Luma" as its parent.
I did copy
"_module.less" from "vendor/magento/theme-frontend-blank/Magento_Theme/web/css/source" to "Magento_Theme/web/css/source/" in my custom theme folder and changed the "_module.less" file but It didnt override styles, so it didnt apply on my webshop.
I deleted the theme files in "/pub/static" and flushed magento cache, with no results.
Does anyone know how to override ".less" / css stylings of the default / luma theme? I want to customize the luma theme, thats why I created my custom theme and now Id like to change some css styles.