CSS color variables, less bold font weight and more (#13567)

* CSS color variables, less bold font weight

- Define color variables for fully saturated colors and apply them where
  it made sense
- Add background color helper classes
- Globally reduce bold font weight from 700 to 500
- Remove border from timeline icons
- Unify dropzone styling
- Various border style consolidations

* attempt to fix test

* another attempt at tests

* fix contains

web_src/less/_organization.less

@@ -117,7 +117,7 @@
       .item {
         margin-left: 0;
         margin-right: 0;
-        border-bottom: 1px solid #eeeeee;
+        border-bottom: 1px solid var(--color-secondary);
 
         .ui.avatar {
           width: 48px;
@@ -137,7 +137,7 @@
         padding: 10px 15px;
 
         &:not(:last-child) {
-          border-bottom: 1px solid #eeeeee;
+          border-bottom: 1px solid var(--color-secondary);
         }
       }
     }
@@ -149,7 +149,7 @@
         line-height: 32px;
 
         &:not(:last-child) {
-          border-bottom: 1px solid #dddddd;
+          border-bottom: 1px solid var(--color-secondary);
         }
 
         .button {
@@ -186,7 +186,7 @@
         margin-right: -14px;
         margin-left: -14px !important;
         padding: 10px;
-        border-bottom: 1px solid #e1e4e8;
+        border-bottom: 1px solid var(--color-secondary);
         border-top: none;
 
         a {