(enhance) Change the style of the inline code

The initial inline code style was very non-obvious.
I eventually figured out I could change the syntax highlighting for the
inline code block with the following change.
https://www.janmeppe.com/blog/how-to-change-code-blocks-minimal-mistakes/
https://mmistakes.github.io/minimal-mistakes/docs/stylesheets/
mmistakes/minimal-mistakes#2808

Basically after the original SCSS is loaded, we make some configuration
changes.
The change exclude this style when the <code> tag is in the header <tag>

ChatGPT helped a little to understand what is going on and come up with
final solution.

assets/css/main.scss

@@ -49,3 +49,9 @@ html {
 .hide-title .page__title {
   display: none;
 }
+
+// Custom styles for inline code
+code.language-plaintext:not(h1 code.language-plaintext):not(h2 code.language-plaintext):not(h3 code.language-plaintext) {
+  color: #d14;
+  border: 1px solid #b6b6b6;
+}