http: optimize HTTP request thread we don't need a mutex at all, in fact all we need is an atomic boolean to signify whether the thread is cancelled. curl options are now for the most part handled by a separate function to keep them in sync between non-threaded and threaded implementations

// WebKit-style focus

.tab-focus() {
  // Default
  outline: thin dotted;
  // WebKit
  outline: 5px auto -webkit-focus-ring-color;
  outline-offset: -2px;
}