MAGETWO-44976: Close button is displayed not aligned on One Page Checkout Storefront popup

Author: Olga Lytvynenko

app/design/frontend/Magento/blank/web/css/source/components/_modals_extend.less

@@ -26,6 +26,8 @@
 @modal-action-close__font-size: 32px;
 @modal-action-close__hover__color: darken(@primary__color, 10%);
 
+@modal-slide-action-close__padding: @modal-slide-header__padding-vertical - 1rem @modal-popup__padding - 1rem;
+
 //
 //  Common
 //  _____________________________________________
@@ -75,7 +77,7 @@
 
     .modal-slide {
         .action-close {
-            padding: @modal-slide-header__padding-vertical @modal-slide__padding;
+            padding: @modal-slide-action-close__padding;
         }
         .page-main-actions {
             margin-top: @modal-slide-header__padding-vertical;

app/design/frontend/Magento/luma/web/css/source/_theme.less

@@ -251,6 +251,7 @@
 
 //  Modal popup
 @modal-action-close__font-size: @font-size__base;
+@modal-slide-action-close__padding: @modal-slide-header__padding-vertical @modal-popup__padding;
 
 //  Checkout tooltip icon
 @checkout-tooltip-icon__font-size: 21px;