From 99e286452ca3bf83606f418763ca36b42a0d3b33 Mon Sep 17 00:00:00 2001
From: Steven Loria <sloria1@gmail.com>
Date: Wed, 15 Jan 2025 15:50:45 -0500
Subject: [PATCH] Add announcement banner (#2781)

---
 docs/_static/custom.css | 7 ++++++-
 docs/conf.py            | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/docs/_static/custom.css b/docs/_static/custom.css
index 28d1ca135..a373a293b 100644
--- a/docs/_static/custom.css
+++ b/docs/_static/custom.css
@@ -12,10 +12,15 @@ h2, h3, h4, h5, h6 {
 
 /* Links */
 
-a:link, a:visited {
+/* Don't change the color of visited links. */
+a:visited {
   color: var(--color-link);
 }
 
+.announcement-content a {
+  color: var(--color-announcement-text);
+}
+
 /* Hide ToC caption text within the main body (but leave them in the side-bar). */
 /* https://github.com/hynek/structlog/blob/b488a8bf589a01aabc41e3bf8df81a9848cd426c/docs/_static/custom.css#L17-L20 */
 #furo-main-content span.caption-text {
diff --git a/docs/conf.py b/docs/conf.py
index 55621e9fd..9e585dd55 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -37,6 +37,7 @@
     "light_logo": "marshmallow-logo-with-title.png",
     "dark_logo": "marshmallow-logo-with-title-for-dark-theme.png",
     "source_repository": "https://github.com/marshmallow-code/marshmallow",
+    "announcement": 'This is the documentation for the unreleased 4.0 version. The latest v3 docs are <a href="https://marshmallow.readthedocs.io/en/3.x-line/">here</a>.',
     "source_branch": "dev",
     "source_directory": "docs/",
     "sidebar_hide_name": True,