First, you know you misspelled “height”, right?
To override css, you can use the “!important” operator. So you’d use:
html,body{height: auto !important;}
Also, you are doing something like this in your functions.php, right?
function changeLoginCSS() { ?>
<style type="text/css">
html,body{height: auto !important;}
</style>
<?php }
add_action( 'login_enqueue_scripts', 'changeLoginCSS' );