Overrode Mark Styles in Placeholder (#3703)

* disabled user select on placeholder

* fixed css property value without quotes

* overrode mark styles in placeholder

Co-authored-by: Cameron Ackerman <cameron_ackerman@selinc.com>

packages/slate-react/src/components/leaf.tsx

@@ -42,6 +42,9 @@ const Leaf = (props: {
             whiteSpace: 'nowrap',
             opacity: '0.333',
             userSelect: 'none',
+            fontStyle: 'normal',
+            fontWeight: 'normal',
+            textDecoration: 'none',
           }}
         >
           {leaf.placeholder as React.ReactNode}