I have created the registration.php, theme.xml,composer.json in app/design/frontend/myvendorname/themename_theme/ and _extends.less in app/design/frontend/myvendorname/themename_theme/web/css/source.
Ran the following commands
rm -r /home/magento/pub/static/* /home/magento/var/view_preprocessed/* /home/magento/var/cache/*
cp /root/.htaccess /home/magento/pub/static/
#re-copying htaccess above to static folder just in case it got lost
magento cache:flush
magento setup:static-content:deploy -f
chown -R www-data:www-data /home/magento
chmod -R 777 /home/magento
So when the magento frontend loads, everything is broken since no style-l or style-m is inherited from luma and no css from _extends.less shows up. The _extends.less only contains body{background-color:yellow;} . I have also tried with renaming _extends.less to _extend.less or _extend.css . In one of the iterations I saw the frontend load properly though WITHOUT my css when I had mistakenly not included the css folder inside the web folder.
What am I doing wrong? I have been at it for the last 2 days!