fix: TOC component overflows the webpage (#209)

src/constants/constants.ts

@@ -13,4 +13,7 @@ export const BANNER_HEIGHT_EXTEND = 30
 export const BANNER_HEIGHT_HOME = BANNER_HEIGHT + BANNER_HEIGHT_EXTEND
 
 // The height the main panel overlaps the banner, unit: rem
-export const MAIN_PANEL_OVERLAPS_BANNER_HEIGHT = 3.5
+export const MAIN_PANEL_OVERLAPS_BANNER_HEIGHT = 3.5
+
+// Page width: rem
+export const PAGE_WIDTH = 75