style(css): Style default values as inline code in argument meta

Add background, border-radius, padding, and font-family to
.argparse-argument-meta .nv to match inline code appearance.

Author: tony

docs/_static/css/argparse-highlight.css

@@ -353,9 +353,13 @@ body:not([data-theme="dark"]) .argparse-argument-name .headerlink:hover:not(:vis
 
 /*
  * Default value styling in metadata
- * Uses .nv (Name.Variable) class for yellow/italic styling consistent with metavars.
+ * Styled like inline code with monokai background.
  */
 .argparse-argument-meta .nv {
+    background: var(--color-inline-code-background);
+    border-radius: .2rem;
+    padding: .325rem .6rem;
+    font-family: var(--font-stack--monospace);
     color: #E5C07B;
     font-style: italic;
 }