Help with CSS customization for version 12

Hello. I am trying to apply our branding to a sugar 12 instance. I am following the guideline from Administration menu. I copied variables.php to custom/themes/clients/base/default/variables.php. The result is a bit ugly (attached in a note). Header menu link does not follow link color declared in variables.php. The search bar does not follow the navigation panel background color, only half of it. Can we tweak a little more? For example I want a linear gradient not a plain background. On v10 we modified custom.less, but in v12 a lot has changed and the UI has been redisgned so we need to keep up with the changes.