oobe-adaptive-dialog: Fix width formula.

Mistakenly used 100% to make content div allocate all free width space
in the portrait mode which is the width of dialog - 2 paddings.

Bug: 1151292
Change-Id: I3374815190d928d4a3b32b3df9d022cc7fef1f3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2628952Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Commit-Queue: Roman Aleksandrov <raleksandrov@google.com>
Cr-Commit-Position: refs/heads/master@{#844069}

chrome/browser/resources/chromeos/login/components/oobe_adaptive_dialog/oobe_adaptive_dialog.html

@@ -87,7 +87,9 @@
         --oobe-adaptive-dialog-content-direction: column;
         --oobe-adaptive-dialog-item-alignment: center;
         --oobe-text-alignment: center;
-        --oobe-adaptive-dialog-content-width: 100%;
+        --oobe-adaptive-dialog-content-width: calc(
+            var(--oobe-adaptive-dialog-width) -
+            2 * var(--oobe-adaptive-dialog-content-padding));
         /* Header takes 40% of the width remaining after applying padding */
         --oobe-adaptive-dialog-header-width: clamp(302px,
             calc(0.4 * (var(--oobe-adaptive-dialog-width) -