<div>
    <label for="username">Username:</label>
    <input type="text" id="username" name="username">
</div>

<div>
    <label for="pass">Password (8 characters minimum):</label>
    <input type="password" id="pass" name="password"
           minlength="8" required>
</div>

<input type="submit" value="Sign in">

label {
    display: block;
    font: 0.9rem 'Fira Sans', sans-serif;
}

input[type='submit'],
label {
    margin-top: 1rem;
}