Fixed icon and button colours in dark mode

refs https://ghost.slack.com/archives/C02G9E68C/p1652957053084759

- Activiy feed filters label colours
- Activiy feed member email address text colour
- . (i) icon when editing newsletters
- colour of edit pencil when editing free tier
- paid tiers 'active' dropdown button colour

ghost/admin/app/styles/layouts/member-activity.css

@@ -46,7 +46,7 @@
     margin: 0;
     padding: 0;
     font-size: 1.4rem;
-    color: #40474f;
+    color: var(--darkgrey-l1);
 }
 
 .gh-member-details-activity-link {
@@ -196,7 +196,7 @@
     display: flex;
     align-items: center;
     justify-content: flex-start;
-    color: #394047;
+    color: var(--darkgrey);
     font-weight: 500;
     font-size: 1.4rem;
     padding: 0.125rem 6rem 0 0.25rem;

ghost/admin/app/styles/layouts/tiers.css

@@ -18,7 +18,7 @@
 
 .gh-contentfilter-menu-trigger-tiers .ember-power-select-selected-item {
     font-weight: 400 !important;
-    color: #394047 !important;
+    color: var(--darkgrey) !important;
 }
 
 .gh-tier-cards {
@@ -55,8 +55,8 @@
 }
 
 .gh-tier-card-edit-button svg {
-    fill: #15171a;
-    color: transparent;
+    /*fill: #15171a;
+    color: transparent;*/
 }
 
 .gh-tier-actions-menu {

ghost/admin/app/styles/patterns/buttons.css

@@ -261,7 +261,7 @@ fieldset[disabled] .gh-btn {
     width: 1em;
     height: 1em;
     margin-right: 0.6em;
-    fill: var(--white);
+    fill: currentColor;
 }
 
 .gh-btn-white svg {

ghost/admin/app/styles/spirit/_icons.css

@@ -85,17 +85,23 @@
 .fill-black-90 g { fill: var(--black-90); }
 
 .fill-darkgrey path,
-.fill-darkgrey g { fill: var(--darkgrey); }
+.fill-darkgrey g, 
+.fill-darkgrey circle { fill: var(--darkgrey); }
 .fill-middarkgrey path,
-.fill-middarkgrey g { fill: var(--middarkgrey); }
+.fill-middarkgrey g,
+.fill-middarkgrey circle { fill: var(--middarkgrey); }
 .fill-midgrey path,
-.fill-midgrey g { fill: var(--midgrey); }
+.fill-midgrey g,
+.fill-midgrey circle { fill: var(--midgrey); }
 .fill-midlightgrey path,
-.fill-midlightgrey g { fill: var(--midlightgrey); }
+.fill-midlightgrey g,
+.fill-midlightgrey circle { fill: var(--midlightgrey); }
 .fill-lightgrey path,
-.fill-lightgrey g { fill: var(--lightgrey); }
+.fill-lightgrey g,
+.fill-lightgrey circle  { fill: var(--lightgrey); }
 .fill-whitegrey path,
-.fill-whitegrey g { fill: var(--whitegrey); }
+.fill-whitegrey g,
+.fill-whitegrey circle { fill: var(--whitegrey); }
 
 /* Shades */
 .fill-blue-l3 path,