Run stylelint --fix

css/private_message_inbox_block.css

@@ -7,9 +7,7 @@
 .block-private-message-inbox-block .private-message-thread:hover {
   background-color: gray;
 }
-.block-private-message-inbox-block
-  .private-message-thread
-  .private-message-inbox-thread-link {
+.block-private-message-inbox-block .private-message-thread .private-message-inbox-thread-link {
   position: absolute;
   top: 0;
   left: 0;

css/private_message_notification_block.css

@@ -22,14 +22,10 @@
   color: #000;
   line-height: 26px;
 }
-.block-private-message-notification-block
-  .unread-threads
-  .private-message-notification-image {
+.block-private-message-notification-block .unread-threads .private-message-notification-image {
   right: 0;
   left: auto;
 }
-.block-private-message-notification-block
-  .unread-threads
-  .private-message-page-link {
+.block-private-message-notification-block .unread-threads .private-message-page-link {
   color: #f00;
 }

css/private_message_thread.css

@@ -18,54 +18,28 @@
   justify-content: flex-start;
   margin: 0 -5px;
 }
-#private-message-page
-  .private-message-thread-full
-  .private-message-recipients
-  span,
-#private-message-page
-  .private-message-thread-full
-  .private-message-recipients
-  article {
+#private-message-page .private-message-thread-full .private-message-recipients span,
+#private-message-page .private-message-thread-full .private-message-recipients article {
   padding: 0 5px;
 }
-#private-message-page
-  .private-message-thread-full
-  .field--name-private-messages
-  .private-message {
+#private-message-page .private-message-thread-full .field--name-private-messages .private-message {
   margin-top: -1px;
   padding: 5px;
   border: solid #ccc 1px;
 }
-#private-message-page
-  .private-message-thread-full
-  .field--name-private-messages
-  .private-message
-  .field--name-created {
+#private-message-page .private-message-thread-full .field--name-private-messages .private-message .field--name-created {
   float: right;
 }
-#private-message-page
-  .private-message-thread-full
-  .field--name-private-messages
-  #load-previous-messages-button-wrapper {
+#private-message-page .private-message-thread-full .field--name-private-messages #load-previous-messages-button-wrapper {
   border: solid #ccc 1px;
 }
-#private-message-page
-  .private-message-thread-full
-  .field--name-private-messages
-  #load-previous-messages-button-wrapper.load-previous-position-before {
+#private-message-page .private-message-thread-full .field--name-private-messages #load-previous-messages-button-wrapper.load-previous-position-before {
   border-bottom: none;
 }
-#private-message-page
-  .private-message-thread-full
-  .field--name-private-messages
-  #load-previous-messages-button-wrapper.load-previous-position-after {
+#private-message-page .private-message-thread-full .field--name-private-messages #load-previous-messages-button-wrapper.load-previous-position-after {
   border-top: none;
 }
-#private-message-page
-  .private-message-thread-full
-  .field--name-private-messages
-  #load-previous-messages-button-wrapper
-  a {
+#private-message-page .private-message-thread-full .field--name-private-messages #load-previous-messages-button-wrapper a {
   display: block;
   text-align: center;
   border-bottom: none;