MC-5405: Column Minimum Height Issues

- fix tab item top border after removing the transparent border from system-border

Author: anthoula

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/tab-item/_default.less

@@ -25,12 +25,12 @@
             background: @color-white;
             content: '';
             height: 1px;
-            left: -1px;
+            left: 0;
             opacity: 1;
             position: absolute;
-            top: -2px;
+            top: -1px;
             visibility: visible;
-            width: calc(~'100% + 2px');
+            width: 100%;
             z-index: auto;
         }