MAGETWO-39422: [UI] Assistance with applying new style for Credit card validation

Author: Oleg Zinoviev

app/design/frontend/Magento/blank/Magento_Checkout/web/css/source/module/checkout/_fields.less

@@ -30,4 +30,38 @@
             }
         }
     }
+    .opc-wrapper {
+        .fieldset {
+            > .field {
+                > .label {
+                    font-weight: @font-weight__regular;
+                }
+            }
+        }
+    }
+}
+
+//
+//  Desktop
+//  _____________________________________________
+
+.media-width(@extremum, @break) when (@extremum = 'min') and (@break = @screen__m) {
+    //  ToDo UI: remove with global blank theme .field.required update
+    .opc-wrapper {
+        .fieldset {
+            > .field {
+                &.required {
+                    position: relative;
+                    > label {
+                        padding-right: 25px;
+                        &:after {
+                            margin-left: @indent__s;
+                            position: absolute;
+                            top: 9px;
+                        }
+                    }
+                }
+            }
+        }
+    }
 }

app/design/frontend/Magento/blank/Magento_Checkout/web/css/source/module/checkout/_shipping.less

@@ -53,11 +53,6 @@
             margin-bottom: @indent__base;
 
             .fieldset {
-                .field {
-                    .label {
-                        font-weight: @font-weight__regular;
-                    }
-                }
                 .note {
                     font-size: @font-size__base;
                     margin-top: @indent__s;

app/design/frontend/Magento/luma/Magento_Checkout/web/css/source/module/checkout/_fields.less

@@ -0,0 +1,33 @@
+// /**
+//  * Copyright © 2015 Magento. All rights reserved.
+//  * See COPYING.txt for license details.
+//  */
+
+//
+//  Variables
+//  _____________________________________________
+
+@checkout-field-validation__border-color: @form-element-validation__border-error;
+
+//
+//  Common
+//  _____________________________________________
+
+& when (@media-common = true) {
+    .field {
+        .control {
+            &._with-tooltip {
+                &:extend(.abs-field-tooltip all);
+            }
+        }
+        &._error {
+            .control {
+                input,
+                select,
+                textarea {
+                    .css(border-color, @checkout-field-validation__border-color);
+                }
+            }
+        }
+    }
+}