diff --git a/core/modules/system/system.base.css b/core/modules/system/system.base.css
index 233c6d7..32fc128 100644
--- a/core/modules/system/system.base.css
+++ b/core/modules/system/system.base.css
@@ -4,6 +4,16 @@
  */
 
 /**
+ * Responsive form text inputs.
+ */
+.form-text {
+  -moz-box-sizing: border-box;
+  -webkit-box-sizing: border-box;
+  box-sizing: border-box;
+  width: 100%;
+}
+
+/**
  * Autocomplete.
  *
  * @see autocomplete.js
@@ -27,9 +37,7 @@
   cursor: default;
   white-space: pre;
 }
-input.form-autocomplete {
-  max-width: 100%;
-}
+
 /* Animated throbber */
 .js input.form-autocomplete {
   background-image: url(../../misc/throbber.gif);