The quickest way to make Visualforce pages styled like Lightning Experience is by incorporating SLDS. This provides consistent styling without rewriting the applications.
Why not other options?
A: Rewriting all Visualforce pages as Lightning components is time-consuming and not efficient.
B: There is no attributeenableLightningin Visualforce.
C: Enabling Lightning Experience compatibility does not apply styling automatically.
Salesforce Lightning Design System (SLDS)