style: selection color (#315)

Author: peterpeterparker

src/lib/styles/global.scss

@@ -12,6 +12,7 @@
 @import "./global/blockquote.scss";
 @import "./global/scrollbar.scss";
 @import "./global/menu.scss";
+@import "./global/selection.scss";
 
 @import "./themes/dark.scss";
 @import "./themes/light.scss";

src/lib/styles/global/selection.scss

@@ -0,0 +1,9 @@
+::selection {
+  background: var(--primary);
+  color: var(--primary-contrast);
+}
+
+::-moz-selection {
+  background: var(--primary);
+  color: var(--primary-contrast);
+}