Few more UI observation (fixes) (#2283)

* fixed bottom border for fabric

* fixed scrollbar

* reverted last

* updated the review comments

* Fixed scroll , updated the home page UI box shadow, header font weight, margin between boxed , subtab underline for fabric fixed

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Co-authored-by: Sakshi Gupta <sakshig@microsoft.com>

src/Explorer/SplashScreen/SplashScreenButton.tsx

@@ -15,7 +15,7 @@ const useStyles = makeStyles({
   button: {
     border: "1px solid var(--colorNeutralStroke1)",
     boxSizing: "border-box",
-    boxShadow: "var(--shadow4)",
+    boxShadow: "rgba(0, 0, 0, 0.25) 0px 4px 4px",
     borderRadius: "4px",
     padding: "32px 16px",
     backgroundColor: "var(--colorNeutralBackground1)",