Question is in the title. I'm used to using camelcase in development and, since there are crossovers with design, was wondering if there are any technical reasons (regardless of opinions) against using it in HTML. Thanks in advance for your replies.
Technically, no, there are no technical issues. Do what you like.
Do try to follow a good style-guide though, like this one from Google. Its section "Class Name Delimiters" says
Separate words in class names by a hyphen.
And its section "Capitailization" says:
All code [the guide is for HTML/CSS, not JS] has to be lowercase: This applies to HTML element names, attributes, attribute values (unless
text/CDATA), CSS selectors, properties, and property values (with the exception of strings).
Examples thus include video-id (note that they converted the word "ID" to lowercase).