Cloudflare won't even let me access the site. But through the Wayback Machine I checked, it's using this: https://developer.mozilla.org/en-US/docs/Web/CSS/user-select
From vendor.css:
div,
i,
span {
-webkit-touch-callout:none;
-webkit-user-select:none;
-khtml-user-select:none;
-moz-user-select:none;
-ms-user-select:none;
user-select:none;
-webkit-tap-highlight-color:var(--constantTransparent)
}