[FIX] website_slides_forum: fix navbar overflow and mobile bg

Linked to task 1958372
Related to PR #32648

addons/website_forum/static/src/scss/website_forum.scss

@@ -220,8 +220,9 @@ img.o_forum_avatar_big {
 }
 
 .o_wforum_elearning_navtabs_container {
-    height: $owprofile-tabs-height;
-    background-color: #66445e;
+    @include media-breakpoint-up(md) {
+        background-color: theme-color('secondary');
+    }
 }
 
 .website_forum {

addons/website_forum/views/website_forum.xml

@@ -52,7 +52,7 @@
 
         <div id="wrap" t-attf-class="container #{website_forum_action}">
             <div class="row">
-                <div class="o_wprofile_email_validation_container mb16 mt16">
+                <div class="o_wprofile_email_validation_container flex-grow-1 mb16 mt16">
                     <t t-call="website_profile.email_validation_banner">
                         <t t-set="redirect_url" t-value="'/forum/%s' % forum.id"/>
                         <t t-set="send_validation_email_message" t-value="'Click here to send a verification email allowing you to participate to the forum.'"/>

addons/website_slides_forum/views/website_slides_forum_templates.xml

@@ -3,7 +3,7 @@
     <template id="website_slides_forum_header" inherit_id="website_forum.header">
         <xpath expr="//div[hasclass('container')]" position="before">
             <t t-if="forum.slide_channel_id">
-                <div class="row o_wforum_elearning_navtabs_container">
+                <div class="o_wforum_elearning_navtabs_container">
                     <div class="container">
                         <ul class="nav nav-tabs o_wprofile_nav_tabs mt-0 flex-nowrap" role="tablist" id="profile_extra_info_tablist">
                             <li class="nav-item">