Yes it is valid.
From the W3Schools website:
The <option> tag also supports the Global Attributes in HTML.
From which the class
attribute is a part of. Please note that often, the option
tag has formatting issues regarding the browser you are using, so styling it can be a little tricky.
EDIT: Since I wrote this answer, it has come to my attention that W3Schools probably isn't the most reliable source of good information. The previous answer isn't at all wrong, but it came from a source that has proven to be somewhat inconsistent/incomplete. As such, I think I should also append a more official link to this subject here.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…