Revert "OOBE - Remove background from EULA ToS"

This reverts commit a6caea96.

Reason for revert: introduces regression https://crbug.com/1124479

Original change's description:
> OOBE - Remove background from EULA ToS
>
> Injects additional CSS into the EULA webview to set the background
> to transparent. This allows Chrome OS to show the inner webview shadows,
> the scrolling shadows, and the rounded corners on the EULA webview.
>
> Fixed: 1061030, 1065275
> Change-Id: Ib58fe9512926f6267344d82d0c5692c9ab3610a2
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216079
> Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
> Commit-Queue: Renato Silva <rrsilva@google.com>
> Cr-Commit-Position: refs/heads/master@{#792620}

TBR=rsorokin@chromium.org,rrsilva@google.com
Bug: 1124479

Change-Id: I9242965f2eb1eebe704cd3ec9b6225adbb5f81e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2396155
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804757}

chrome/browser/resources/chromeos/login/oobe_eula.js

@@ -19,11 +19,7 @@ const EULA_FONTS_CSS = {
   code: `body * {
         font-family: Roboto, sans-serif !important;
         font-size: 13px !important;
-        background-color: transparent !important;
         line-height: 20px !important;}
-       body {
-        background-color: transparent !important;
-       }
        body h2 {
          font-size: 15px !important;
          line-height: 22px !important;}`