Fix Bug 1510551-Align checkbox with EOY and Newsletter snippet strings (#4594)

content-src/asrouter/templates/EOYSnippet/_EOYSnippet.scss

@@ -42,6 +42,7 @@
   }
 
   .monthly-checkbox-container {
+    display: flex;
     width: 100%;
   }
 

content-src/asrouter/templates/SubmitFormSnippet/_SubmitFormSnippet.scss

@@ -67,6 +67,7 @@
     font-size: 12px;
     color: var(--newtab-text-secondary-color);
     margin-top: 10px;
+    display: flex;
     flex: 0 0 100%;
   }