diff --git a/core/themes/bartik/css/components/form.css b/core/themes/bartik/css/components/form.css
index dd5ac0c..f3e7326 100644
--- a/core/themes/bartik/css/components/form.css
+++ b/core/themes/bartik/css/components/form.css
@@ -67,6 +67,7 @@ input {
   margin: 2px 0;
   padding: 4px;
   /* Keep form elements from overflowing their containers. */
+  width: 100%;
   max-width: 100%;
   box-sizing: border-box;
 }
diff --git a/core/themes/seven/css/components/form.css b/core/themes/seven/css/components/form.css
index f74eb74..1ef84ad 100644
--- a/core/themes/seven/css/components/form.css
+++ b/core/themes/seven/css/components/form.css
@@ -160,6 +160,7 @@ input.form-time,
 textarea.form-textarea {
   box-sizing: border-box;
   padding: .3em .4em .3em .5em; /* LTR */
+  width: 100%;
   max-width: 100%;
   border: 1px solid #b8b8b8;
   border-top-color: #999;