These are some CSS snippets that alter the Sugarcane format. Insert them directly into a "stylesheet" passage in your Twine games to use them. They might work with Jonah as well, with some slight adjustments.

I don't consider myself a graphic designer or web designer, so these are to be regarded solely as amateur efforts.

"Hypercane 1.0"
Features: Sidebar is converted to a top bar (minus Share); vaguely resembles System 6, but nowhere near enough for true aficionados.

body {
  margin: 10% 0 10% 0;
}
#passages{
  margin: 0;
  padding: 0;
  border: 0;
}
.passage, #sidebar * {
  font-family: "Geneva", "Helvetica",sans-serif;
  color:#000;
  text-align:left;
}
.passage {
  border-radius: 0.2em;
  width: 60%;
  margin: auto;
  padding: 2em;
  font-size:1.5rem;
  background-color:#fff;
  border: solid #000 0.05em;
  box-shadow: #000 0.5em 0.5em 0;
}
a.internalLink, a.externalLink {
  border: solid #000 0.05em;
  white-space: nowrap;
  padding: 0.1em 0.2em 0.1em 0.2em;
  border-radius: 0.5em;
  color:#000;
}
a.internalLink:hover, a.externalLink:hover {
  text-decoration: none;
  box-shadow: #000 0 0 0 0.1em;
  color:#000;
}
a.internalLink:active, a.externalLink:active {
  color: #fff;
  background-color:#000;
}
body {
  background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAQAAAAEAQMAAACTPww9AAAABGdBTUEAALGPC/xhBQAAAAZQTFRFAAAA////pdmf3QAAAA5JREFUeF5jOACEBgwGAAnIAeGomjuiAAAAAElFTkSuQmCC);
}
#sidebar {
  position:absolute;
  top:0px;
  left:0px;
  width:99.2%;
  overflow-x:hidden;
  background-color:#fff;
  border-bottom: solid #000 1px;
}
#sidebar * {
  color: #000 !important;
  font-size:1.5rem;
  background-color:clear !important;
  display:inline !important;
}
#sidebar a:hover, #sidebar #snapback:hover,  #sidebar #restart:hover {
  text-decoration:underline !important;
}
#sidebar a:active, #sidebar #snapback:active,  #sidebar #restart:active  {
  color:#fff !important;
  font-size:1.5rem;
  background-color:#000 !important;
  display:inline !important;
}
#sidebar li, #sidebar li span {
  margin-left: 1rem;
  margin-right: 1rem;
}
#sidebar a, #sidebar a:hover {
  border: 0 !important;
  box-shadow: none;
}
.menu {
  background-color:#fff;
  color:#000;
  opacity:1;
  font-size: 1.5rem;
  border: solid #000 1px;
  box-shadow: #000 0.1em 0.1em 0;
}
.menu div:hover {
  background-color:#000;
  color:#fff;
}
#credits, #share, #titleSeparator {
  display:none !important;
}

"Closed In"
Features: No sidebar; Enormous screen-filling font size designed for very terse stories; Font should scale down on mobile devices.

body {
  margin: 2%;
}
#passages{
  margin: 0;
  padding: 0;
  border: 0;
  width:96%;
  margin: auto;
}
.passage {
  font-size:6em; 
  color: #888;
  text-shadow: #888 0 0 0.05em;
}
@media screen and (max-width: 960px) {
  .passage {
    font-size: 4em;
  }
}
@media screen and (max-width: 640px) {
  .passage {
    font-size: 3em;
  }
}
a.internalLink, a.externalLink {
  color: #eee;
  text-shadow: #eee 0 0 0.07em;
}
a.internalLink:hover, a.externalLink:hover {
  color: #fff;
  text-decoration: none;
  text-shadow: #fff 0 0 0.09em;
}
#sidebar {
	display:none;
}

"Orange Highlight"
Features: No sidebar; External links are a different colour to internal links.

body {
  margin: 5% 0 0 0;
  background-color:#000;
}
#passages{
  margin: 0;
  padding: 0;
  border: 0;
}
.passage {
  font-family: "Times New Roman",serif;
  text-align:left;
  color:#000;
  width: 40em;
  padding: 2em;
  font-size:3em;
  background-color:#fff;
  background: -webkit-linear-gradient(left, #aaa 0%,#fff 19%);
  background: linear-gradient(to right, #aaa 0%,#fff 19%);
}
a.internalLink {
  color:#620;
  background-color:#fd5;
}
a.externalLink {
  color:#602;
  background-color:#f5d;
}
a.internalLink:hover {
  color:#410;
  background-color:#fa0;
  text-decoration: none;
}
a.externalLink:hover {
  color:#401;
  background-color:#f0a;
  text-decoration: none;
}
a.internalLink:active {
  color:#140;
  background-color:#af0;
  text-decoration: none;
}
a.externalLink:active {
  color:#104;
  background-color:#a0f;
  text-decoration: none;
}
#sidebar {
  display:none;
}

"ZX Spectwine"
Features: No sidebar; is a little bit garish.

body {
  margin: 0;
  background-color:#000;
}
#passages {
  margin: 0;
  padding: 0;
  border: 0;
}
.passage {
  width: 40%;
  min-width: 26em;
  font-family: Helvetica, sans-serif;
  letter-spacing: 0.1em;
  font-size:1.8em;
  margin: 10% 0 10% 10%;
  box-shadow: orangered 0 0 0 0.4em;
  border: gold solid 0.4em;
  padding:0.4em;
  background-color:lawngreen;
  border-radius: 1em;
}
.passage .content, .passage .body {
  margin: 0;
  padding: 1.5em;
  background-color:#000;
  box-shadow: lawngreen 0 0 0 0.4em;
  border: cornflowerblue solid 0.4em;
  border-radius:0.2em;
  text-align:left;
  font-family: sans-serif;
  font-weight: lighter;
  color:#fff;
}

a.internalLink, a.externalLink {
  background-color:#506070;
  box-shadow: #304050 0.1em 0.1em 0 0.1em;
  position:relative;
  left: -0.1em;
  top: -0.1em;
  padding: 0.2em 0.3em 0.2em 0.3em;
  font-weight: lighter;
  color:#fff;
}
a.internalLink:hover, a.externalLink:hover {
  color:#fff;
  background-color:slategray;
  text-decoration:none;
}
a.internalLink:active, a.externalLink:active {
  box-shadow: none;
  background-color:#304050;
  position:static;
  margin: 0;
}
#sidebar {
  display:none;
}

body {
  margin: 0;
  padding: 0;
}
#passages {
  margin: 0 5% 0 5%;
  padding: 2.5% 0 5% 0;
  border-left: saddlebrown solid 1.5em;
  height:auto;
  background: #3d1d08;
  background: -webkit-radial-gradient(center, ellipse cover,  #3d1d08 0%,#000000 80%);
  background: radial-gradient(ellipse at center,  #3d1d08 0%,#000000 80%);
}
.header {
  width: 25%;
  border-top: saddlebrown solid 0.1em;
  margin: auto;
  padding: 0 0 2.5% 0;
}
.passage {
  margin: 2em;
  font-family: "Georgia", serif;
  font-size:2.2em; 
  color: peru;
  text-shadow: sienna 0.05em 0.05em 0.05em;
}
a.internalLink, a.externalLink {
  color: burlywood;
  text-shadow: peru 0.05em 0.05em 0.05em;
}
a.internalLink:hover, a.externalLink:hover {
  color: cornsilk;
  text-decoration: none;
  text-shadow: peru 0.05em 0.05em 0.05em;
}
#sidebar {
	display:none;
}