Docs: Broken layout on landing page (offline style)

This commit fixes the broken layout. Wrapping the divs of
col-1 (content) and col-2(sidebar) classes with a container with
`display:flex` does the job.

Fixes: QTBUG-129178
Change-Id: I6867b178e5a1acf6a4fbd5302a857e5f3ca0a62f
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Kai Köhne <kai.koehne@qt.io>
(cherry picked from commit d39c9d3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 148f1a5)

doc/global/template/style/offline.css

@@ -724,6 +724,9 @@ Landing page
     vertical-align: top;
 }
 
+.landing {
+    display: flex;
+}
 
 .landing h2 {
     background-color: transparent;
@@ -738,19 +741,14 @@ Landing page
 }
 
 .col-1 {
-    display: inline-block;
     white-space: normal;
     width: 70%;
-    height: 100%;
-    float: left;
 }
 
 .col-2 {
-    display: inline-block;
     white-space: normal;
     width: 20%;
     margin-left: 5%;
-    position: relative;
     top: -20px;
 }