OOBE Assistant: Adapt the dialog size for different resolutions

Bug: 1001458
Change-Id: Id88dd59b8a97df515c3bbaa3f4e5cea3c356eda2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1844982
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704101}

chrome/browser/resources/chromeos/assistant_optin/assistant_shared_styles.css

@@ -9,15 +9,20 @@ a {
 }
 
 oobe-dialog {
-  height: calc(640px - var(--caption-bar-height));
+  height: calc(var(--oobe-dialog-host-height, 640px) -
+               var(--caption-bar-height));
 }
 
 .container {
-  height: 496px;
-  overflow: hidden;
-  padding: calc(60px - var(--caption-bar-height)) 64px 0 64px;
+  box-sizing: border-box;
+  height: 100%;
+  padding-bottom: 0;
+  padding-inline-end: var(--oobe-dialog-content-padding, 64px);
+  padding-inline-start: var(--oobe-dialog-content-padding, 64px);
+  padding-top: calc(var(--oobe-dialog-content-padding, 60px) -
+                    var(--caption-bar-height));
   position: absolute;
-  width: 640px;
+  width: 100%;
 }
 
 .line {