Improve upgrade CTA for dark mode, remove some now-unused variables from notes restyles

_includes/upgrade-cta.html

@@ -1,5 +1,5 @@
 <div class="docker-upgrade-cta" role="alert">
-  <div class="docker-upgrade-cta__heading">This feature requires a Pro or Team plan.</div>
+  <div class="docker-upgrade-cta__heading">{{include.header-text}}</div>
 
   {{ include.body | markdownify }}
 

_scss/_night-mode.scss

@@ -25,7 +25,7 @@ body.night {
     div#side-toc-title {
         color: $white;
     }
-    a {
+    a:not(.btn) {
         color: $primary-links-night;
     }
     .header {

_scss/_upgrade-cta.scss

@@ -1,5 +1,6 @@
 .docker-upgrade-cta {
   background-color: $orange-10;
+  color: $body-text; // we want this irrespective of light/dark mode
 
   padding: 16px 25px;
   margin: 0 0 20px;

_scss/_variables.scss

@@ -31,7 +31,6 @@ $bg-card:                 hsl(  0,   0%, 100%);
 
 // notes, warnings
 $note-color:              hsl(206,  82%,  43%);
-$note-bg-color:           hsl(206,  83%,  98%);
 $important-color:         hsl( 35,  91%,  35%);
 $warning-color:           hsl(  2,  58%,  54%);
 
@@ -58,12 +57,6 @@ $bg-footer-landing-night: hsl(214, 100%,  20%);
 $bg-component-night:      hsl(203,  44%,  10%);
 $bg-card-night:           hsl(203,  33%,   8%);
 
-// notes, warnings
-$note-color-night:        hsl(180,   1%,  83%);
-$note-bg-color-night:     hsl(203,  35%,  19%);
-$important-color-night:   hsl( 35,  90%,  62%);
-$warning-color-night:     hsl(  2, 100%,  74%);
-
 $active-sidebar-night:    hsl(203,  85%,   79%);
 
 $bg-search-results-night: hsla(0,    0%,    4%, 0.95);

test.md

@@ -663,12 +663,19 @@ It will render like this  with a colored sidebar and icon:
 
 Use the `upgrade-cta.html` include to render a CTA asking the user to upgrade their plan. There are two parameters:
 
-- `target-url`: This will typically be something like https://www.docker.com/pricing, possibly with a utm code.
+- `target-url`: This is what the upgrade button will link to. Will typically be something like `https://www.docker.com/pricing`, possibly with a utm code.
+- `header-text`: The text shown in the bolded header at the top of the CTA. Only accepts strings, no Markdown support.
 - `body`: This forms the body of the CTA. It accepts Markdown. To use multi-line bodies, use named captures as explained in [the Jekyll docs](https://jekyllrb.com/docs/includes/#passing-parameter-variables-to-includes).
 
+{% raw %}
+```liquid
+{% include upgrade-cta.html
+  body="Upgrade to gain access to this feature"
+  header-text="This feature is restricted to X and Y plans"
+  target-url="https://www.example.com/
+%}
 ```
-{% include upgrade-cta.html body="Upgrade to gain access to this feature" target-url="https://www.example.com/" %}
-```
+{% endraw %}
 
 ## Code blocks