mysqli_set_charset($conn, "utf8mb4");
mysqli_query($conn, "SET NAMES utf8mb4");

<form method="post" style="width:300px;margin:100px auto;background:#fff;padding:20px;border-radius:8px;text-align:center">
<h3>LOGIN</h3>
<input name="usuario" placeholder="Usuário" required><br><br>
<input type="password" name="senha" placeholder="Senha" required><br><br>
<button name="entrar">Entrar</button>
</form>