Introduce "Heavier" theme, with thicker fonts

Partly prompted by this piece:

https://backchannel.com/how-the-web-became-unreadable-a781ddc711b6

editions/prerelease/tiddlers/sidebarwidth.tid

@@ -0,0 +1,2 @@
+title: $:/themes/tiddlywiki/vanilla/metrics/sidebarwidth
+text: 450px

editions/prerelease/tiddlers/theme.tid

@@ -1,3 +1,3 @@
 title: $:/theme
 
-$:/themes/tiddlywiki/snowwhite
+$:/themes/tiddlywiki/heavier

editions/prerelease/tiddlywiki.info

@@ -20,6 +20,7 @@
 		"tiddlywiki/starlight",
 		"tiddlywiki/seamless",
 		"tiddlywiki/centralised",
+		"tiddlywiki/heavier",
 		"tiddlywiki/tight",
 		"tiddlywiki/readonly"
 	],

editions/tw5.com/tiddlers/system/theme.tid

@@ -1,3 +1,3 @@
 title: $:/theme
 
-$:/themes/tiddlywiki/snowwhite
+$:/themes/tiddlywiki/heavier

editions/tw5.com/tiddlywiki.info

@@ -14,6 +14,7 @@
 		"tiddlywiki/seamless",
 		"tiddlywiki/centralised",
 		"tiddlywiki/tight",
+		"tiddlywiki/heavier",
 		"tiddlywiki/readonly"
 	],
 	"languages": [

themes/tiddlywiki/heavier/base.tid

@@ -0,0 +1,68 @@
+title: $:/themes/tiddlywiki/heavier/base
+tags: [[$:/tags/Stylesheet]]
+
+\rules only filteredtranscludeinline transcludeinline macrodef macrocallinline
+
+html body h1,
+html body h2,
+html body h3,
+html body h4,
+html body h5,
+html body h6 {
+	font-weight: 600;
+}
+
+html body strong {
+	font-weight: 700;
+}
+
+html body .tc-tiddler-frame .tc-tiddler-body {
+	font-weight: 500;
+}
+
+html body button.tc-tiddlylink,
+html body a.tc-tiddlylink {
+	font-weight: 700;
+}
+
+html body a.tc-tiddlylink-shadow {
+	font-weight: 700;
+}
+
+html body a.tc-tiddlylink-shadow.tc-tiddlylink-resolves {
+	font-weight: 500;
+}
+
+html body button.tc-tag-label,
+html body span.tc-tag-label {
+	font-weight: 500;
+}
+
+html body .tc-sidebar-header .tc-title a.tc-tiddlylink-resolves {
+	font-weight: 500;
+}
+
+html body .tc-menu-list-count {
+	font-weight: 700;
+}
+
+html body .tc-view-field-name {
+	font-weight: 400;
+}
+
+html body .tc-site-title,
+html body .tc-titlebar {
+	font-weight: 500;
+}
+
+html body .tc-subtitle {
+	font-weight: 500;
+}
+
+html body .tc-tiddler-missing .tc-title {
+	font-weight: 500;
+}
+
+html body .tc-tab-buttons button {
+	font-weight: 500;
+}

themes/tiddlywiki/heavier/plugin.info

@@ -0,0 +1,9 @@
+{
+	"title": "$:/themes/tiddlywiki/heavier",
+	"name": "Heavier",
+	"author": "JeremyRuston",
+	"core-version": ">=5.0.0",
+	"plugin-type": "theme",
+	"description": "Heavier font theme",
+	"dependents": ["$:/themes/tiddlywiki/snowwhite"]
+}