Style the block placeholder element

apps/block_scout_web/assets/css/components/_loading-spinner.scss

@@ -38,7 +38,7 @@
 .loading-spinner-small {
   display: inline-block;
   position: relative;
-  top: -0.05em;
+  top: -0.125em;
   margin: auto 0.5em auto 0;
   width: 1em;
   height: 1em;

apps/block_scout_web/assets/js/pages/block.js

@@ -110,13 +110,15 @@ if ($blockListPage.length) {
 function placeHolderBlock(blockNumber) {
   return `
     <div class="tile tile-type-block fade-up" data-selector="place-holder" data-block-number="${blockNumber}">
-      <div class="row">
+      <div class="d-flex">
-        <div class="col-md-6">
+        <span class="loading-spinner-small ml-1 mr-4">
-          <span>${blockNumber}</span>
+          <span class="loading-spinner-block-1"></span>
-        <div>
+          <span class="loading-spinner-block-2"></span>
-        <div class="col-md-6">
+        </span>
-          Block Mined, awaiting import...
         <div>
+          <div class="tile-title">${blockNumber}</div>
+          <div> Block Mined, awaiting import...</div>
+        </div>
       </div>
     </div>
   `