docs: Add design touch-ups (#17505)

This PR adds several design tweaks to elements of the documentation,
most notably swapping the heading title font from `PPAgrandir` to
`Lora`, which makes the docs consistent with the new website. Aside from
this, there's also some tiny, low-hanging content adjustments to a few
pages.

--- 

Release Notes:

- N/A

docs/theme/fonts/fonts.css

@@ -1,13 +1,6 @@
 /* Open Sans is licensed under the Apache License, Version 2.0. See http://www.apache.org/licenses/LICENSE-2.0 */
 /* Source Code Pro is under the Open Font License. See https://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=OFL */
-
 /* open-sans-300 - latin_vietnamese_latin-ext_greek-ext_greek_cyrillic-ext_cyrillic */
-@font-face {
-  font-family: "Agrandir";
-  font-style: normal;
-  font-weight: 400;
-  src: url("PPAgrandir-Regular.woff2") format("woff2");
-}
 
 @font-face {
   font-family: "IA Writer Quattro S";
@@ -15,3 +8,10 @@
   font-weight: 400;
   src: url("iAWriterQuattroS-Regular.woff2") format("woff2");
 }
+
+@font-face {
+  font-family: "Lora";
+  src: url("Lora.var.woff2") format("woff2-variations");
+  font-weight: 100 900;
+  font-style: normal;
+}