diff -u b/core/modules/system/templates/field.html.twig b/core/modules/system/templates/field.html.twig
--- b/core/modules/system/templates/field.html.twig
+++ b/core/modules/system/templates/field.html.twig
@@ -36,14 +36,14 @@
 the tempate file {{ attributes.class }} is providing a placeholder for mddules
 that wants to add classes to a field.
 #}
-{% set cssclass %}
+{% set css-class %}
 field field-name--{{ field_name }} field-type--{{ field_type }} field-label--{{ field_label }} {{ attributes.class}}
 {% endset %}
 
 {% if multiple and label_visible %}
 {#
   First we check if its a multiple value field and if it have a visible label.
-    <div class="field field--multiple {{ cssclass }}">
+    <div class="field field--multiple {{ css-class }}">
       <div class="field__label">Label</div>
       <div class="field-items">
         <div class="field_item">Data</div>
@@ -51,7 +51,7 @@
       </div>
     </div>
 #}
-  <div class="field--multiple {{ cssclass }}"{{ attributes }}>
+  <div class="field--multiple {{ css-class }}"{{ attributes }}>
     <div class="field__label"{{ title_attributes }}>{{ label }}</div>
     <div class="field__items"{{ content_attributes }}>
       {% for delta, item in items %}
@@ -63,13 +63,13 @@
 {% elseif multiple and not label_visible %}
 {#
   We check if its a multiple value field and if it have a visible label.
-    <div class="field field--multiple field-items {{ cssclass }}">
+    <div class="field field--multiple field-items {{ css-class }}">
         <div class="field_item">Data</div>
         <div class="field_item">Data</div>
       </div>
     </div>
 #}
-  <div class="field--multiple field__items {{ cssclass }}"{{ attributes }}{{ content_attributes }}>
+  <div class="field--multiple field__items {{ css-class }}"{{ attributes }}{{ content_attributes }}>
     {% for delta, item in items %}
       <div class="field__item"{{ item_attributes[delta] }}>{{ item }}</div>
     {% endfor %}
@@ -78,12 +78,12 @@
 {% elseif not multiple and label_visible %}
 {#
   We Check if its a single field and it have its label visbile
-    <div class="field field--single {{ cssclass }}">
+    <div class="field field--single {{ css-class }}">
       <div class="field_label">Data</div>
       <div class="field_item">Data</div>
     </div>
 #}
-  <div class="field--single{{ cssclass }}"{{ attributes }}>
+  <div class="field--single {{ css-class }}"{{ attributes }}>
     <div class="field__label"{{ title_attributes }}>{{ label }}</div>
     {% for delta, item in items %}
       <div class="field__item"{{ content_attributes }}{{ item_attributes[delta] }}>{{ item }}</div>
@@ -93,13 +93,13 @@
 {% elseif not multiple and not label_visible %}
 {#
   Now check if the field is a single field and dont have a label shown
-    <div class="field field--single field__item{{ cssclass }}">
+    <div class="field field--single field__item{{ css-class }}">
       data
     </div>
   The holy grail of single field data!
 #}
   {% for delta, item in items %}
-    <div class="field--single field__item {{ cssclass }}"{{ attributes }}{{ item_attributes[delta] }}>
+    <div class="field--single field__item {{ css-class }}"{{ attributes }}{{ item_attributes[delta] }}>
       {{ item }}
     </div>
   {% endfor %}