Fix line number width in code preview (#31307)

Line numbers were using some hacky CSS `width: 1%` that did nothing to
the code rendering as far as I can tell but broken the inline preview in
markup when line numbers are greater than 2 digits. Also I removed one
duplicate `font-family` rule (it is set below in the `.lines-num,
.lines-code` selector.

web_src/css/base.css

@@ -1001,8 +1001,6 @@ overflow-menu .ui.label {
   padding: 0 8px;
   text-align: right !important;
   color: var(--color-text-light-2);
-  width: 1%;
-  font-family: var(--fonts-monospace);
 }
 
 .lines-num span.bottom-line::after {