fix(markdown): remove invalid `.highlight` class

src/scss/markdown.scss

@@ -1,13 +1,12 @@
 .markdown-body {
   color: var(--xm-c-regular);
   font-family: var(--xm-font-display) !important;
-  pre:not(.shiki, .highlight) {
+  pre:not(.shiki) {
     margin: 0;
     padding: 0;
     background: transparent;
   }
-  .shiki,
-  .highlight {
+  .shiki {
     margin: .5rem 0;
     font-size: 1.05rem;
     font-family: var(--xm-font-code) !important;

src/scss/variables/_colors.scss

@@ -13,6 +13,6 @@ $quote-border: hsla(0deg 0% 50% / .3);
 $thead-border: #d1d5db;
 $tr-border: #e5e7eb;
 
-// Shiki (code highlight)
+// Shiki (code highlighting)
 $shiki-light: #f8f8f8;
 $shiki-dark: #0e0e0e;