message: feat(theme): improve navbar alignment
diff: .navbar-right,
  .navbar-center {
  display: flex;
  + flex: 1;
  align-items: center;
  > * {
  }
  }
  +.navbar-left {
  + justify-content: start;
  +}
  +
  +.navbar-center {
  + justify-content: center;
  +}
  +
  +.navbar-right {
  + justify-content: end;
  +}
  +
  // docsearch fix
  // stylelint-disable selector-class-pattern
  .DocSearch {
  