Improve rendering style of markdown in the mdbook (#26616)

book.toml

@@ -18,6 +18,7 @@ create-missing = false
 # Remove the numbers that appear before each item in the sidebar, as they can
 # get quite messy as we nest deeper
 no-section-label = true
+additional-css = ["docs/css/custom.css"]
 
 # The source code URL of the repository
 git-repository-url = "https://github.com/vector-im/element-web"

docs/css/custom.css

@@ -0,0 +1,14 @@
+/* Prevent collapsible headings from wrapping onto two lines eagerly */
+summary > h1,
+summary > h2,
+summary > h3,
+summary > h4,
+summary > h5,
+summary > h6 {
+    display: inline-block;
+}
+
+/* Prevent longer checkbox lists from wrapping eagerly */
+input + p {
+    display: inline;
+}