Dark theme for line numbers in blame view (#12632)

web_src/less/themes/theme-arc-green.less

@@ -1446,11 +1446,13 @@ input {
   background-color: #bbbbbb !important;
 }
 
-.lines-commit {
+.lines-commit,
+.blame .lines-num {
   background: #2e323e !important;
 }
 
-.bottom-line {
+.bottom-line,
+.bottom-line:after {
   border-color: #4e525e !important;
 }