If you find you prefer to use a different font family that the defaulted one to your theme, you can use CSS to apply your preferred font family to the storefront.

For example, if you are want to replace the Default font used in the Elements theme with the one used in the Mr Tea's theme (Font-family "Lato"), navigate to the storefront menu then select CSS then enter the following:

h1, h2, h3, h4, h5, body.catalog.sidebar aside h2, body.product-review-page .product-review h2, .titles, .title {
    font-family: "Lato";
}

Here's an example of how this will appear in the CSS editor:

Related Documentation

Font SFO