A very good tutorial for dropdowns using CSS without JavaScript is at https://stevespages.org.uk/codenotes/codeexamples/nav/dotted-squirrel/
CSS Selectors https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors
https://git-scm.com/ has documentation for git including the man pages and the Pro Git book written by Scott Chacon and Ben Straub.
I ammended a commit that I had pushed to github because their was a typo in the commit message. I could not then push the ammended commit to github. In order to do so I had to git merge origin/main. This is explained here: https://www.koskila.net/how-to-git-merge-upstream/
Airbnb Style guide.
JavaScript The Definitive Guide by David Flanagan. A comprehensive well reviewed treatment.
https://blog.jgrossi.com/2013/creating-your-first-composer-packagist-package/
Algorithms by Cormen, Leiserson, Rivest, Stein. A thousand pages and in its 4th edition, a classic.
Leetcode https://dev.to/snj/leetcode-problems-for-beginners-5enm
PEP 8 Style guide is at https://pep8.org/
Google Style guide.
Abbreviated to reST.
rst-cheatsheet https://github.com/ralsina/rst-cheatsheet/blob/master/rst-cheatsheet.rst is a useful reference.
http://www1.udel.edu/evelyn/SQL-Class1/oSQLclass1All.html
sphinx-doc.org Eg.https://www.sphinx-doc.org/en/master/usage/quickstart.html
Database Design for Mere Mortals by Michael Hernandez is a classic.
SQL Queries for Mere Mortals by John L Viescas This book is OK but has unconvincing file and database naming conventions. It also at least one database example which has a redundant schema and inconsistent data in it.
StanforOnline has some excellent videos on relational algebra and SQL. See: https://www.edx.org/school/stanfordonline Jennifer Widom is an excellent teacher in the videos.
MySQL tutorial: https://www.mysqltutorial.org
For a good SQLite tutorial, including using the PHP interface, see https://www.sqlitetutorial.net/
What is SVG Animation? https://www.smashingmagazine.com/2020/09/smashing-podcast-episode-24/
Various stuff on SVG https://www.petercollingridge.co.uk/tutorials/
Creating dynamic SVG elements with JavaScript https://www.motiontricks.com/creating-dynamic-svg-elements-with-javascript/
GreenSock https://greensock.com/gsap/
Interactive Animations with CSS and JavaScript on LinkedIn
CSS-TRICKS. Using SVG https://css-tricks.com/using-svg/
stackoverflow.com Ask questions and try to improve your coding by answering other people's questions.
LeetCode has Over 1000 problems that can be solved in any of about 10 languages. The are classified as easy, medium or hard. Freemium.