Stylesheet for specific page overwritten by standard css
Add weight to the CSS:

drupal_add_css(drupal_get_path('theme', 'subtheme') . "/css/login.css", array('weight' =&gt; 100));


See the drupal_add_css() API page for more info. The group option may also be relevant as this also affects the weight.

Also if the specificity of a rule in style.css overrules a rule in login.css it won't matter what order the CSS files are included.