Apply newsletter background color to template preview images

assets/css/src/box.styl

@@ -101,3 +101,6 @@
 [data-type="standard"] .mailpoet_thumbnail
   background-image: url("data:image/svg+xml;charset=utf-8,%3Csvg%20version%3D%221.1%22%20id%3D%22Layer_1%22%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20xmlns%3Axlink%3D%22http%3A%2F%2Fwww.w3.org%2F1999%2Fxlink%22%20x%3D%220px%22%20y%3D%220px%22%20viewBox%3D%220%200%2070%2070%22%20enable-background%3D%22new%200%200%2070%2070%22%20xml%3Aspace%3D%22preserve%22%3E%3Cpath%20fill%3D%22%23ffffff%22%20fill-rule%3D%22evenodd%22%20clip-rule%3D%22evenodd%22%20d%3D%22M62.751%2C65.368L43.923%2C50.955l18.832-14.377l-5.395-4.118v-3.479l5.983%2C4.568%20v3.479l0.166%2C26.269C63.51%2C64.089%2C63.198%2C64.783%2C62.751%2C65.368z%20M31.433%2C49.5l-15.955-12v-30c0-1.657%2C1.339-3%2C2.992-3h33.905%20c1.652%2C0%2C2.992%2C1.343%2C2.992%2C3v30l-15.955%2C12H31.433z%20M18.469%2C35.5H33.5v-2H18.469V35.5z%20M18.469%2C31.5H33.5v-2H18.469V31.5z%20M18.469%2C27.5H33.5v-2H18.469V27.5z%20M38.406%2C7.5H18.469v14h19.937V7.5z%20M52.375%2C7.5H40.408v2h11.967V7.5z%20M52.375%2C11.5H40.408v2%20h11.967V11.5z%20M52.375%2C15.5H40.408v2h11.967V15.5z%20M52.375%2C19.5H40.408v2h11.967V19.5z%20M52.375%2C25.5H37.5v2h14.875V25.5z%20M52.375%2C29.5H37.5v2h14.875V29.5z%20M52.375%2C33.5H37.5v2h14.875V33.5z%20M26.14%2C17.192L28.442%2C9.5l3.277%2C6.571l1.71-2.571l2.992%2C6%20h-2.992h-3.989h-0.997H25.45h-4.986l3.989-4L26.14%2C17.192z%20M22.469%2C12.5h-1c-0.552%2C0-1-0.448-1-1v-1c0-0.552%2C0.448-1%2C1-1h1%20c0.552%2C0%2C1%2C0.448%2C1%2C1v1C23.469%2C12.052%2C23.021%2C12.5%2C22.469%2C12.5z%20M26.795%2C50.955L8.05%2C65.305c-0.419-0.574-0.55-1.41-0.55-2.174%20V37.015l-0.015%2C0.011v-3.479l5.998-4.579v3.479L8.017%2C36.62L26.795%2C50.955z%20M29.137%2C52.659v-0.157h12.462v0.144l0.047-0.036%20L59.73%2C66.5H10.989l18.084-13.889L29.137%2C52.659z%22%2F%3E%3C%2Fsvg%3E%0A")
 
+.mailpoet_boxes_preview
+  margin: -10px
+  padding: 10px 20px

assets/js/src/newsletters/templates.jsx

@@ -153,7 +153,7 @@ define(
       handleShowTemplate: function(template) {
         MailPoet.Modal.popup({
           title: template.name,
-          template: '<img src="{{ thumbnail }}" />',
+          template: '<div class="mailpoet_boxes_preview" style="background-color: {{ body.globalStyles.body.backgroundColor }}"><img src="{{ thumbnail }}" /></div>',
           data: template,
         });
       },