add the link into your custom header:
like:
<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Lato:wght@300&display=swap" rel="stylesheet">
and in your custom css something like:
*{
font-family: Lato, serif;
}