doc: emphasize security warning in vm module doc

Refs: #40718

Author: Trott

doc/api/vm.md

@@ -9,8 +9,10 @@
 <!-- source_link=lib/vm.js -->
 
 The `vm` module enables compiling and running code within V8 Virtual
-Machine contexts. **The `vm` module is not a security mechanism. Do
-not use it to run untrusted code.**
+Machine contexts.
+
+<span class="critical">The `vm` module is not a security
+mechanism. Do not use it to run untrusted code.</span>
 
 JavaScript code can be compiled and run immediately or
 compiled, saved, and run later.

doc/api_assets/style.css

@@ -29,6 +29,7 @@
   --background-color-highlight: var(--white-smoke);
   --color-brand-primary: var(--gray6);
   --color-brand-secondary: var(--green1);
+  --color-critical: var(--red1);
   --color-fill-app: var(--white);
   --color-fill-side-nav: var(--gray6);
   --color-links: var(--green1);
@@ -40,6 +41,7 @@
 
 .dark-mode {
   --background-color-highlight: var(--black2);
+  --color-critical: var(--red2);
   --color-fill-app: var(--black1);
   --color-fill-side-nav: var(--black3);
   --color-links: var(--green5);
@@ -165,6 +167,11 @@ em code {
   line-height: 1.5rem;
 }
 
+.critical, .critical code {
+  color: var(--critical);
+  font-weight: 700;
+}
+
 li.version-picker {
   position: relative;
 }