templates/login.html

{% extends "base.html" %}
{% block content %}
<div class="container py-5">
  <div class="card p-4 mx-auto" style="max-width: 400px;">
    <h2 class="mb-3">Login</h2>
    {% if error %}<div class="alert alert-danger">{{ error }}</div>{% endif %}
    <form method="POST" action="{{ url_for('login') }}">
      <input type="text" name="username" class="form-control mb-3" placeholder="Username" required>
      <input type="password" name="password" class="form-control mb-3" placeholder="Password" required>
      <button type="submit" class="btn btn-gradient w-100">Login</button>
    </form>
    <p class="mt-3">No account? <a href="{{ url_for('signup') }}">Sign up</a></p>
  </div>
</div>
{% endblock %}