Files.app: Make cloud backup dropdown button on toolbar more skinny.

BUG=483716
TEST=manually

Review URL: https://codereview.chromium.org/1140653003

Cr-Commit-Position: refs/heads/master@{#329346}

ui/file_manager/file_manager/foreground/css/file_manager.css

@@ -423,7 +423,12 @@ body.check-select #gear-button {
 }
 
 #cloud-import-details-button {
-  -webkit-margin-start: -15px;
+  -webkit-margin-start: -11px;
+  width: 24px;
+}
+
+#cloud-import-details-button core-icon {
+  margin: 8px 4px;
 }
 
 #cloud-import-details {