Fixes to codeblock (pre)

- Set a value for top and bottom margins.
- Fix the line height being too large.

_includes/styles/base.scss

@@ -98,6 +98,8 @@ code {
 }
 
 pre {
+  margin-top: 1rem;
+  margin-bottom: 1rem;
   padding: 1rem;
   border-radius: 5px;
   display: block;
@@ -106,9 +108,9 @@ pre {
   page-break-inside: avoid;
   word-wrap: break-word;
   font-family: var(--font--mono);
+  line-height: initial;
   code {
     font-size: 1rem;
-    line-height: normal;
     padding: 0;
     border-radius: 0;
     background-color: transparent;