A question from a nervous candidate, “What should I wear for the viva? I want to make the right first impression on my examiners!”
Except that’s not the first impression. Your examiners’ first impression is your thesis. They get their first impression long before they meet you in the viva.
Wear something that helps you to feel confident: there are far more important questions to grapple with than what should you wear.
What have you written? What did you do? What does it mean and why does it matter?
And what impression do you hope your thesis will make?