.btn-extra { margin-top: 10px; }<div style="display: flex; justify-content: center; margin-top: 100px;"> <div style="text-align: center; background-color: transparent; color: #fff; font-size: 12px; padding: 10px;"> <form action="login.php" method="post"> <div class="form-group"> <label for="username">login</label> <input type="text" id="username" name="username" class="form-control"> </div> <div class="form-group"> <label for="password">pass</label> <input type="password" id="password" name="password" class="form-control"> </div> <button type="submit" class="btn btn-primary btn-extra">join</button> </form> </div><img src="/images/autumn.jpg" alt="bg" width="300" height="100"></div>