fix: correct formatting of border style in CSS guide

Author: danieldanielecki

data/blog/software-development/web-development/frontend/cascading-style-sheets-css/combining-border-top-border-right-border-left-border-bottom-in-css-a-complete-guide.mdx

@@ -281,7 +281,7 @@ The border shorthand property has been a fundamental CSS feature since the early
 Common causes:
 - Border width set to 0
 - Border color matching the background
-- Border style set to 'none'
+- Border style set to `none`
 - Element being covered by another element
 
 ### Inconsistent Border Rendering