Is HTML or CSS open source like PHP or Python?
For example PHP itself: PHP source link in GITHUB
CodePudding user response：
You must understand the difference between the specification (documentation, idea) and the implementation (interpreter, compiler, engine). Refer to https://softwareengineering.stackexchange.com/questions/238724/what-license-is-html-released-under for more detailed answers.
CodePudding user response：
HTML
HTML only provides tags around text but other than that html files are practically just text files with extra markers. These tags are then parsed by the parser of the browser you use and displayed in a certain way. The easiest example of this is probably the <strong></strong>, <i></i> and <b></b> tags. These tags only purpose is to modify the text within them to look different. But the strong tag looks different on different browsers. Some browsers make text bold while others do other changes. This shows you that the browser really is the interpreter and there are not always strict rules on what tags must do. The current standard (html5) was created by a group called the WHATWG. See more information also here https://www.w3.org/html/. and their own website https://html.spec.whatwg.org/multipage/. They have a github https://github.com/whatwg/html and I believe you can make changes if they accept your merge requests.
CSS
CSS is also not really a language. CSS is prescribed by the css working group their members are publicly known. https://www.w3.org/Style/CSS/members. If you scroll through the list you will see most of these people are engineers from big tech companies. They do have a github for css it is used for people to post issues. https://github.com/w3c/csswg-drafts. I do believe you can create a merge request although i am unsure.
Summary
In short yes they are basically opensource. However changes to either of these repositories even when accepted and merged will not work untill browsers have implemented the changes.
note
I am not an expert by any means I googled most of my information. I could be wrong about multiple things.