The search button in the top bar was lost its style on the stackexchange.com -> Newsletters page. The search button style is fine on the other pages.
GIF for the same:
When an inspect the element, the following style was overridden in the
.top-bar .searchbar .btn-topbar-primary CSS class, that caused the styling issue:
background-color: #0095ff; padding: 0 12px;
Mozilla Firefox: 59.0b10 (64-bit)
Google Chrome: Version 64.0.3282.167 (Official Build) (64-bit)
OS: Windows 7