feat(design): improve design of backup-needed-modal

src/sass/views/includes/modals/backup-confirm-modal.scss

@@ -1,3 +0,0 @@
-#backup-confirm-modal{
-  
-}

src/sass/views/includes/modals/backup-needed-modal.scss

@@ -0,0 +1,12 @@
+#backup-needed-modal{
+  .button.button-secondary {
+    font-size: 14px;
+    margin-top: 0;
+  }
+  .button {
+    display: block;
+    margin-right: auto;
+    margin-left: auto;
+    margin-top: 1rem;
+  }
+}

src/sass/views/includes/modals/modals.scss

@@ -73,5 +73,5 @@
   background: rgba(0, 0, 0, .8);
 }
 
-@import "backup-confirm-modal";
+@import "backup-needed-modal";
 @import "screenshot-warning-model";

www/views/includes/backupNeededPopup.html

@@ -3,25 +3,11 @@
     <div class="popup-modal-header-img-warning popup-modal-header-img"></div>
   </div>
   <div class="popup-modal-content popup-modal-content-warning">
-    <div class="text-center">
-      <h5 translate>Backup Needed</h5>
-      <p translate>Now is a good time to backup your wallet. If this device is lost, it is impossible to access your funds without a backup.</p>
-      <div class="row">
-        <div class="col">
-          <button
-            class="button button-clear expand"
-            ng-click="close()"
-            translate>Not now
-          </button>
-        </div>
-        <div class="col">
-          <button
-            class="button button-clear expand"
-            ng-click="doBackup()"
-            translate>OK
-          </button>
-        </div>
-      </div>
+    <div>
+      <div class="popup-modal-heading" translate>Backup Needed</div>
+      <div class="popup-modal-message" translate>Now is a good time to backup your wallet. If this device is lost, it is impossible to access your funds without a backup.</div>
+      <button class="button button-clear" ng-click="doBackup()" translate>Backup now</button>
+      <button class="button button-secondary button-clear" ng-click="close()" translate>Remind me later</button>
     </div>
   </div>
 </div>