Updated font-size variable and standardize #ToDo UI

Author: gelanivishal

app/design/adminhtml/Magento/backend/web/app/setup/styles/less/lib/_buttons.less

@@ -99,8 +99,8 @@
     background-color: transparent;
     border: none;
     color: @link__color;
-    font-family: @btn__base__font-size;
-    font-size: 1.5rem; // ToDo UI: Check font-size and standardize
+    font-family: @font-family__base;
+    font-size: @base__font-size;
 
     &:hover,
     &:active,