Re-implement columns shortcode as markdown list

layouts/_shortcodes/columns.html

@@ -1,4 +1,6 @@
 {{- $ratio := (split (.Get "ratio") ":") -}}
+{{- if strings.Contains .InnerDeindent "<--->" -}}
+{{ warnf "Columns shortcode seprator '<--->' is deprecated, use markdown list instead." -}}
 <div class="book-columns flex flex-wrap{{ with .Get "class" }} {{ . }}{{ end }}">
 {{ range $index, $content := split .InnerDeindent "<--->" }}
   {{- $grow := default 1 (index $ratio $index) -}}
@@ -7,3 +9,13 @@
   </div>
 {{ end }}
 </div>
+{{ else }}
+<div class="book-columns book-columns-{{ .Ordinal }} {{ with .Get "class" }}{{ . }}{{ end }}">
+  <style>{{- range $index, $grow := $ratio -}}
+    .book-columns-{{ $.Ordinal }}>ul>li:nth-child({{ $index | add 1 }}){
+      flex-grow: {{ $grow }};
+    }
+  {{ end -}}</style>
+  {{ .Inner | safeHTML }}
+</div>
+{{ end -}}