Unable to add a new theme variable

Permalink
version: 5.7.5.8

In my styles.xml I added a new variable header-site-tag of type "type"
<style name="Site Title" variable="header-site-title" type="type" />
      <style name="Site Tag" variable="header-site-tag" type="type" />

I then added some defaults to my theme's defaults.less:
@header-site-tag-type-color: #75ca2a;
@header-site-tag-type-font-weight: 400;
@header-site-tag-type-font-size: 2.3em;
@header-site-tag-type-text-transform: none;
@header-site-tag-type-font-family: 'Titillium Web';


The new variable shows up when I edit the theme design, but when I click on it, I get a messed up dialog. (See attached). Other "type" variables work fine. Did I miss a step?

1 Attachment