Change "Security Phrase" font-weight

Author: neer17

Diff for: res/css/_common.scss

@@ -138,6 +138,12 @@ input[type=search]::-webkit-search-results-decoration {
 input::placeholder,
 textarea::placeholder {
     opacity: initial;
+    font-weight: 400;
+}
+input::-moz-placeholder,
+textarea::-moz-placeholder {
+    opacity: .6;
+    font-weight: 400;
 }
 
 input[type=text], input[type=password], textarea {