Is it permissible for a wife to give her husband a gift on his birthday or their anniversary, without celebrating these days?

"Exchange gifts, for a gift removes ill feelings from the chest." A Muslim is encouraged to give gifts to his brethren. This is especially emphasized for spouses to strengthen the bond and affection between them. However, this should not take the form of a celebration for an unlawful holiday, as celebrating birthdays, weddings, or anniversaries are innovations and newly invented matters.

So, a wife gifts her husband, and a husband gifts his wife. This is legally مطلوب (desirable/recommended) and naturally acceptable. However, it is not permissible to hold celebrations and glorify occasions for which Allah has sent down no authority.