Change font size for Product Titles

Hi, I set the fonts with CSS code for my storefront theme. This is the one for H1:
h1 {
font-family: ‘Libre Baskerville 38px’, serif;
}

But I find that too large for my product pages and want to reduce those title fonts.
I’ve tried a few css codes, but they are not working. This is what I’ve been working with

h1 .product_title .entry_title {
font-family: ‘Libre Baskerville 20px’, serif;
}

Appreciate any help with this.