What does vendor lock-in mean?Vendor lock-in is when a company or a services forces you to continue using their product or makes switching away overly complicated. Many website builder or cloud providers sadly tend to apply this strategy. It's not only a computer science issue, but you probably have experienced it in life also.
How to prevent vendor lock-in?
In a general sense, try using products that follow open standards. Free standards are not controlled by one company and are most times documented so everyone can develop products for them. For example the HyperText Markup Language (HTML) is a an open standard not controlled by one single company, but by the WHATWG (w3c previously).
How about Mame?
For CSS we are using bonsai.css
And yes we offer hosting your website, but you have no disadvantage choosing your own hosting provider. You can even directly deploy to Amazon Web Services or Digital Ocean from Mame.