Let \( x \) be the total number of cards sold for Mother's Day. According to the problem, 4% of the total number of cards sold is equal to 33 cards. We can express this relationship mathematically as:
\[ 0.04x = 33 \]
To solve for \( x \), we can divide both sides of the equation by 0.04:
\[ x = \frac{33}{0.04} \]
Calculating the right-hand side:
\[ x = 33 \div 0.04 = 33 \times 25 = 825 \]
Thus, the total number of cards sold for Mother's Day is
\[ \boxed{825} \]