_content/css: set img max width to 100%

Fixes golang/go#65139

Change-Id: I9284fb5d2aae5f4dcff2e422f163381aa19fdb09
Reviewed-on: https://go-review.googlesource.com/c/website/+/556416
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
diff --git a/_content/css/styles.css b/_content/css/styles.css
index eea617d..377d3b1 100644
--- a/_content/css/styles.css
+++ b/_content/css/styles.css
@@ -869,6 +869,9 @@
   padding: 0.5rem 1.75rem;
   border-radius: 4px;
 }
+.Article img {
+  max-width: 100%;
+}
 .CopyPaste {
   display: flex;
   align-items: center;