fix(theme): use faux italics only with web fonts (#1581)

Author: brc-dd

src/client/theme-default/styles/base.css

@@ -26,7 +26,7 @@ body {
   color: var(--vp-c-text-1);
   background-color: var(--vp-c-bg);
   direction: ltr;
-  font-synthesis: style;
+  font-synthesis: none;
   text-rendering: optimizeLegibility;
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;

src/client/theme-default/styles/fonts.css

@@ -1,5 +1,9 @@
 /* webfont-marker-begin */
 @import url('https://fonts.googleapis.com/css2?family=Inter:wght@100..900&display=swap');
+
+html body {
+  font-synthesis: style;
+}
 /* webfont-marker-end */
 
 @font-face {