Voir la source de MediaWiki:Vector.css

/* Le CSS placé ici affectera les utilisateurs de l’habillage Vector. */

.btn {
  display: inline-block;
  padding: 6px 12px;
  margin-bottom: 0;
  font-size: 14px;
  font-weight: normal;
  line-height: 1.428571429;
  text-align: center;
  white-space: nowrap;
  vertical-align: middle;
  cursor: pointer;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
       -o-user-select: none;
          user-select: none;
  background-image: none;
  border: 1px solid transparent;
  border-radius: 4px;
}
.btn:focus {
  outline: thin dotted;
  outline: 5px auto -webkit-focus-ring-color;
  outline-offset: -2px;
}
.btn:hover,
.btn:focus {
  color: #333;
  text-decoration: none;
}
.btn:active,
.btn.active {
  background-image: none;
  outline: 0;
  -webkit-box-shadow: inset 0 3px 5px rgba(0, 0, 0, .125);
          box-shadow: inset 0 3px 5px rgba(0, 0, 0, .125);
}

.btn-primary {
  color: #fff;
  background-color: #428bca;
  border-color: #357ebd;
}
.btn-primary:hover,
.btn-primary:focus,
.btn-primary:active,
.btn-primary.active,
.open .dropdown-toggle.btn-primary {
  color: #fff;
  background-color: #3276b1;
  border-color: #285e8e;
}
.btn-primary:active,
.btn-primary.active,
.open .dropdown-toggle.btn-primary {
  background-image: none;
}