Form etiketini kapatmamışsınız bundan kaynaklı olabilir (</form>).
<body id="register_bg">
<div id="register">
<div class="sign-in-wrapper">
<aside>
<figure>
<a href="index.html"><img src="img/logo_sticky.svg" width="140" height="35" alt=""></a>
</figure>
<div class="access_social">
<a href="#0" class="social_bt facebook">Login with Facebook</a>
<a href="#0" class="social_bt google">Login with Google</a>
</div>
<div class="divider"><span>Or</span></div>
<?=@$cevap?>
<form method="post">
<div class="form-group">
<input class="form-control" type="text" name="kadi" placeholder="Kullanıcı Adınız">
<i class="icon_mail_alt"></i>
</div>
<div class="form-group">
<input class="form-control" type="password" name="pass" id="password" placeholder="Şifreniz">
<i class="icon_lock_alt"></i>
</div>
<div class="clearfix add_bottom_15">
<div class="checkboxes float-left">
<label class="container_check">Beni hatırla
<input type="checkbox">
<span class="checkmark"></span>
</label>
</div>
<div class="float-right"><a id="forgot" href="#0">Forgot Password?</a></div>
</div>
<input type="submit" value="Giriş Yap" class="btn_1 full-width mb_5">
<div class="text-center mt-2"><small>Don't have an acccount? <strong><a href="register.html">Sign Up</a></strong></small></div>
</form>
</div>
<div class="copy">© 2020 FooYes</div>
</aside>
</div>
<!-- /login -->
<!-- COMMON SCRIPTS -->
<script src="js/common_scripts.min.js"></script>
<script src="js/common_func.js"></script>
<script src="assets/validate.js"></script>
</body>
</html>
form etiketini ekledim yine aynı hocam