Style `kbd`, `code` & `pre` elements in GFM"

What does this MR do and why?

Adjusts slightly the monospace elements kbd, code, pre. In the current code version:

• kbd is changed from 11px to 12px and is slightly vertical adjusted
• code is changed from 12.6px to 14px
• pre is changed from 13px to 14px

Screenshots or screen recordings

kbd

Before font-size 11px	After (new font) font-size 12px, adjusted vertical-align

code

Text before code is 14px Inter

Before (90% font-size) - 12.6.px	After (new font) (90% font-size) - 12.6.px	After (new font) - 12px	After (new font) - 14px ( - my favourite)

pre

example borrowed from MDN

Before - font-size: 13px	After (new font) - font-size: 14px

How to set up and validate locally

Follow the instructions from this MR to apply new fonts.

Insert the following code into the markdown field - e.g. I've used project's README. Go to any project page, update README file with the following content

#  testing kbd, code, pre with new mono font

### kbd
<kbd>Ctrl</kbd>Key CTRL

### code

Some text before the code <code>console.log('test')</code>

### pre
<pre role="img" aria-label="ASCII COW">
    ___________________________
&lt; I'm an expert in my field (pre example). &gt;
    ---------------------------
        \   ^__^
        \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||
</pre>

Related to #381554 (closed)

app/assets/stylesheets/startup/startup-dark.scss

@@ -764,7 +764,7 @@ kbd {
   font-size: 0.75rem;
   line-height: 10px;
   color: var(--gray-700, #bfbfc3);
-  vertical-align: middle;
+  vertical-align: unset;
   background-color: var(--gray-10, #1f1e24);
   border-width: 1px;
   border-style: solid;