diff --git a/CHANGES b/CHANGES
index 5ce96bac1..db12b571a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -32,6 +32,7 @@ Bugs fixed
   an attribute and module that are same name
 * #7806: viewcode: Failed to resolve viewcode references on 3rd party builders
 * #7838: html theme: List items have extra vertical space
+* #7878: html theme: Undesired interaction between "overflow" and "float"
 
 Testing
 --------
diff --git a/sphinx/themes/basic/static/basic.css_t b/sphinx/themes/basic/static/basic.css_t
index e0f24c8a1..a22ef80d4 100644
--- a/sphinx/themes/basic/static/basic.css_t
+++ b/sphinx/themes/basic/static/basic.css_t
@@ -15,6 +15,12 @@ div.clearer {
     clear: both;
 }
 
+div.section::after {
+    display: block;
+    content: '';
+    clear: left;
+}
+
 /* -- relbar ---------------------------------------------------------------- */
 
 div.related {
@@ -328,8 +334,8 @@ p.sidebar-title {
     font-weight: bold;
 }
 
-div.admonition, div.topic, pre, div[class|="highlight"] {
-    clear: both;
+div.admonition, div.topic, blockquote {
+    clear: left;
 }
 
 /* -- topics ---------------------------------------------------------------- */
@@ -338,7 +344,6 @@ div.topic {
     border: 1px solid #ccc;
     padding: 7px;
     margin: 10px 0 10px 0;
-    overflow-x: auto;
 }
 
 p.topic-title {
@@ -353,7 +358,6 @@ div.admonition {
     margin-top: 10px;
     margin-bottom: 10px;
     padding: 7px;
-    overflow-x: auto;
 }
 
 div.admonition dt {
@@ -378,6 +382,15 @@ div.admonition > :last-child {
     margin-bottom: 0;
 }
 
+div.sidebar::after,
+div.topic::after,
+div.admonition::after,
+blockquote::after {
+    display: block;
+    content: '';
+    clear: both;
+}
+
 /* -- tables ---------------------------------------------------------------- */
 
 table.docutils {
@@ -680,6 +693,10 @@ pre {
     overflow-y: hidden;  /* fixes display issues on Chrome browsers */
 }
 
+pre, div[class|="highlight"] {
+    clear: both;
+}
+
 span.pre {
     -moz-hyphens: none;
     -ms-hyphens: none;