[DefaultOffline]: New fonts and remove border radius.

Since this is an offline page, we can't use any fonts
that need to be downloaded (and the way it was specified
didn't work anyway). So, as requested by UX, we switch
to the system default sans serif font, and increase the
text just a bit to make the error message more obvious.

Also, using a border radius doesn't work for all icons,
for example the gCalendar one (which is circular and the
corners would get cut off). So, we'll stick to rectangular
ones.

(cherry picked from commit 1d78df8)

Bug: 1410786, 1280518
Change-Id: I279b61404cf639876ae3842aedb0a32bf8bb4eb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4198147
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Chase Phillips <cmp@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1098921}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4207887
Owners-Override: Daniel Yip <danielyip@google.com>
Reviewed-by: Daniel Yip <danielyip@google.com>
Auto-Submit: Finnur Thorarinsson <finnur@chromium.org>
Cr-Commit-Position: refs/branch-heads/5481@{#824}
Cr-Branched-From: 130f3e4-refs/heads/main@{#1084008}

components/web_app_resources/web_app_default_offline.css

@@ -33,12 +33,12 @@
   transform: translate(-50%, -50%);
 }
 .icon {
-  border-radius: 50%;
   height: 160px;
   width: 160px;
 }
 .message {
-  font-family: 'Google Sans';
+  font-family: 'system-ui', sans-serif;
+  font-size: 18px;
   text-align: center;
   width: 80%;
 }