feat: ensure text remains visible during webfont load

The easiest way to avoid showing invisible text while custom fonts
load is to temporarily show a system font. By including
`font-display: swap` in your font style. It's worth mentioning that
not all major browsers support font-display: swap, so you may need
to do a bit more work to fix the invisible text problem.

_sass/yat/_base.scss

@@ -17,6 +17,7 @@ body {
   font-family: $base-font-family;
   font-weight: $base-font-weight;
   font-size: #{$base-font-size};
+  font-display: swap;
   line-height: #{$base-line-height};
   color: $text-color;
   background-color: $background-color;