If you want to change style of Site Title, but want to prevew changes before saving them, you can use this code to Website Tools > Custom CSS.
The code will run on Edit Mode only, it won’t run on Live Mode.
body.sqs-edit-mode div.header-display-mobile a#site-title { font-size: 30px; color: #f1f; font-family: monospace; letter-spacing: 3px; }
Result
(Edit mode)
(Preview/Live Mode)