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 probably won't work with Jonah, though.

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

Click here for live previews of all these stylesheets!

"Muet"
This requires Twine 1.4. The background image is not included - but if you add an embedded image with the name "background", it will be used by this stylesheet! Also, this has no sidebar, only the StoryTitle, StorySubtitle and StoryAuthor.

@import url(http://fonts.googleapis.com/css?family=Alegreya+Sans:300|Oxygen:400,700&subset=latin,latin-ext);

html {
  background: [img[background]] fixed, dodgerblue;
  background-size: cover;
  min-height: 100%;
  height:100%;
}
body {
  background-color: rgba(0,0,0,0.4);
  background-attachment: fixed;
  margin: 0;
  padding: 0% 15% 0% 5em;
  font-size: 100%;
  font-family: Oxygen, "Century Gothic", sans-serif !important;
  font-weight: 300;
  min-height: 100%;
}
#sidebar, #passages {
  padding-top: 4em;
  padding-bottom: 0em;
}
#passages {
  margin-left: 60%;
  padding-left: 5%;
  width: 50%;
  min-height: 100%;
  padding-bottom: 0;
  margin-bottom: 0;
  border: 0;
}
#passages::before {
  border-left: 3px solid rgba(255,255,255,0.2);
  position:fixed;
  height:100%;
  left: 50%;
  top:0;
  content:'';
}
.passage {
  margin: 0px;
  color: white;
  opacity: 0.7;
  font-size: 100%;
  text-align:justify;
  margin:auto;
  padding: 0px 0px 5em 0px;
}
.passage a {
  color: AliceBlue;
  opacity: 1;
}
.passage a:hover {
  color: white;
  text-decoration: none;
  border-bottom: 1px white solid;
}
.passage a:visited {
  color: Thistle;
}
#sidebar {
  left: 1em;
  width: 50%;
  font-family: "Alegreya Sans","Century Gothic",sans-serif !important;
}
#sidebar li {
  color: white !important;
  text-align: center;
  opacity: 0.3;
}
#sidebar #storyTitle {
  font-size: 4em;
  line-height:0.8em;
}
#sidebar > :not(.storyElement) {
  display:none;
}
/* Shrink the page when viewed on devices with a low screen width */
@media screen and (max-width: 1600px) {
  .passage, #sidebar { font-size: 90%; }
}
@media screen and (max-width: 1200px) {
  #sidebar { font-size: 70%;}
  .passage { font-size: 85%;}
}
@media screen and (max-width: 960px) {
  #sidebar { position: relative; width: 100%;}
  #passages { margin: 0; padding: 5%; width: 90%; border: 0; }
}

"Simple Centered"
The "simple" stylesheets are designed to be shorter and more customisable than the others. This one simply consists of passage text, centered horizontally AND vertically inside the window, along with a colour gradient background. See the code comments for places where colours and values can easily be changed.

html {
  width: 100%;

  /* Vertical colour gradient */
  background-image: linear-gradient(to bottom,  black, midnightblue);
  background-image: -webkit-linear-gradient(top,  black, midnightblue);
  background-attachment: fixed;

  /* Fallback colour */
  background-color: midnightblue;

  /* Vertical centering */
  height: 100%;
  display: table;
}
body {
  /* Remove default styles */
  font-size: 100%;
  background-color: transparent;
  margin: 0;

  /* Vertical centering */
  height:100%;
  display:table-cell;
  vertical-align: middle;
}
#passages {
  border-left: 0px;
  margin: 0;
  /* Keep a gap at the top and bottom of the page,
      when the text is longer than the window's height. */
  padding: 5% 0;
}

.passage {
  /* Passage width */
  width: 60%;
  /* Horizontal centering */
  margin: 0 auto;

  /* Text formatting */
  color: white;
  font-size: 100%;
  text-align:center;
}

/* No sidebar */
#sidebar {
  display:none;
}

/* Links */
a.internalLink, a.externalLink {
  color: cornflowerblue;
}
a.internalLink:hover, a.externalLink:hover {
  color: lightskyblue;
  text-decoration: none;
}

/* Shrink the page when viewed on devices with a low screen width */
@media screen and (max-width: 960px) {
  .passage { font-size: 90%; width: 70%; }
}
@media screen and (max-width: 840px) {
  .passage {  font-size: 87.5%; width: 80%; }
}
@media screen and (max-width: 720px) {
  .passage { font-size: 75%; width: 90%; }
}

"Simple Box"
Displays the passage text in a box, centered in the upper middle of the page, in front of a colour gradient.
See the code comments for colours and values that can be customised.

html {
  /* Vertical colour gradient */
  background-image: linear-gradient(to bottom,  gainsboro, silver);
  background-image: -webkit-linear-gradient(top,  gainsboro, silver);
  background-attachment: fixed;

  /* Fallback colour */
  background-color: silver;
}
body {
  /* Remove default styles */
  background-color: transparent;
  margin: 10% 0 0 0;
  font-size: 100%;
  /* Used to center the box */
  text-align: center;
}

#passages {
  /* Box background (white with 70% opacity) */
  background-color: rgba(255, 255, 255, 0.7);

  /* Border */
  border: 2px solid white;

  /* Rounded corners */
  border-radius: 1em;

  /* Box width */
  width: 60%;

  /* Center the box */
  display: inline-block;
  min-height: 40%;
  margin:auto;
  margin-bottom: 5%;
  padding: 0px;
}

.passage {
  margin: 0px;
  /* Inner margin within the box */
  padding: 2em;

  /* Text formatting */
  color: black;
  font-size: 100%;
  text-align:justify;
}

/* No sidebar */
#sidebar {
  display:none;
}

/* Links */
a.internalLink, a.externalLink {
  color: royalblue;
}
a.internalLink:hover, a.externalLink:hover {
  color: deepskyblue;
  text-decoration: none;
}

/* Shrink the page when viewed on devices with a low screen width */
@media screen and (max-width: 960px) {
  .passage { font-size: 90%;}
  #passages { width: 70%; }
}
@media screen and (max-width: 840px) {
  .passage {  font-size: 87.5%; }
  #passages { width: 80%; }
}
@media screen and (max-width: 720px) {
  .passage { font-size: 75%; }
  #passages { width: 90%; }
}

"Squillions"
"It's a Twine game that you can imagine James Bond playing." ? Ian Bogost.

head {
  box-shadow: inset 0px 0px 30em #bbb;
  width:100%;
  height:100%;
  display:block;
  position:fixed;
}
head * {
  display:none;
}
body {
  background-color:#fff;
  margin: 0;
  text-align:center;
}
#passages {
  border-left: 0;
  margin: 0;
  padding: 0;
  line-height:100vh;
}
.passage {
  position:absolute;
  top: 0;  bottom: 0;  left: 0;  right: 0;
  width: 75%;
  height: 75%;
  margin:auto;
  font: bold 6em/1.25em Helvetica, "Helvetica Neue", Arial, sans-serif;
  color: #000;
  letter-spacing: -0.05em;
  text-align:center;
}
#sidebar {
  display:table;
  position:fixed;
  top: 0; left: 0;
  width:100%;
  height:100%;
}
#sidebar #title {
  display:table-cell; 
  vertical-align:middle;
  text-align:center;
}
#sidebar #title #storyTitle {
  font: bold 12em/1.25em Helvetica, "Helvetica Neue", Arial, sans-serif;
  letter-spacing: -0.05em;
  color:rgba(0,0,0,0.15);
}
#title :not(#storyTitle){
  display:none;
}
#storymenu, #snapback, #restart, #share, #credits {
  display:none;
}
a.internalLink:hover, a.externalLink:hover {
  color:#de0000 !important;
  text-decoration: none;
}
a.internalLink:nth-child(3n), a.externalLink:nth-child(3n) {
  color: #666;
}
a.internalLink:nth-child(3n+1), a.externalLink:nth-child(3n+1) {
  color: #777;
}
a.internalLink:nth-child(3n+2), a.externalLink:nth-child(3n+2) {
  color: #888;
}
@media screen and (max-width: 960px) {
  body { font-size: 50%; }
}
@media screen and (max-width: 840px) {
  body { font-size: 40%; }
}
@media screen and (max-width: 720px) {
  body { 
    font-size: 30%;
  }
}

"The Earth's Story Illustrated"
Best used with a dissolve transition.
This stylesheet is capable of displaying a 480-pixels-tall scene image above every passage's text! You can set scene images using Tag CSS. To assign, say, the image "classroom_afternoon" to the tag "classroom", simply create a stylesheet tagged "stylesheet classroom" and put this in it:

.passage .header {
  background-image: [img[classroom]];
}

And then tag various passages with "classroom" to use the image.
To have multiple images overlaid on each other, add multiple img declarations separated by commas, in order from frontmost to rearmost:

.passage .header {
  background-image: [img[character-funnycry]], [img[classroom]];
}

That's how you do it!

#sidebar {
  display:none;
}
body {
  margin: 0;
  padding: 0;
  height:100%;
}
#passages {
  margin:0;
  padding: 0;
  height:100%;
}
#passages * {
  box-sizing: border-box;
  -moz-box-sizing: border-box;
}
.passage {
  position:relative;
  width: 60%;
  font-size:2em;
  font-family: "Lucida Sans Typewriter", Consolas, Monaco, monospace;
  margin: 2em auto 0 auto;
}
.passage .header {
  width:100%;
  height:480px;
  min-height: 480px;
  border: #fff double 0.5em;
  border-radius: 1em;
  margin: 0 auto 1.5em auto;
  padding: 0;
  background-position: center;
  background-repeat: no-repeat;
}
.passage .content {
  top: 500px;
  width:100%;
  border: #fff double 0.5em;
  border-radius: 1em;
  padding: 1em;
}
a.internalLink, a.externalLink {
  border-bottom: solid #fff 1px;
  color:#eee;
  font-weight:normal;
}
a.internalLink:hover, a.externalLink:hover {
  text-decoration:none;
  border-bottom: none;
  color:#000;
  background-color:#fff;
  font-weight:normal;
  padding-left: 0;
}
a.internalLink:active, a.externalLink:active {
  border-bottom: 0;
}
@media screen and (max-width: 960px) {
  .passage {
    font-size: 1.5em;
  width: 75%;
  }
}
@media screen and (max-width: 640px) {
  .passage {
    font-size: 1.25em;
  width: 95%;
  }
}

"Remembering the 90's"
Best used with an instant passage transition.

body {
  background:LightGrey;
  color: #000;
  font: medium "Times New Roman", Times, serif;
  margin: auto;
  padding: 8px;
}
#passages {
  margin: auto;
  border: 0;
  padding: 0;
}
.header, .footer {
  border: 1px inset;
  margin: 0.5rem auto;
}
.passage {
  font: inherit;
  line-height: inherit;
  margin: auto;
}
.passage ul {
  padding: 0;
  text-align: left;
}
.passage li {
  display:inherit;
  margin: 0;
}
a, #sidebar #snapback, #sidebar #restart, #sidebar #share, .menu div {
  font-weight:inherit !important;
  text-decoration: underline !important;
  color: #00F !important;
}
a.visited {
  color: #7F007F;
}
#sidebar {
  font: inherit !important;
  position:static;
  width: auto;
  list-style: disc outside;
}
#sidebar ul {
  padding: inherit;
}
#sidebar li {
  color: inherit;
  text-align:inherit;
  margin:inherit;
  display:inline;
}
#sidebar #titleSeparator {
  display:none;
}
#sidebar #title, #sidebar #title:hover {
  color:inherit;
}
#sidebar #storyTitle, #sidebar #storyTitle:hover {
  font-size: 2rem;
  margin: .67rem 0;
  font-weight:bold;
}
#sidebar #storySubtitle {
  font-size: inherit;
  font-weight:bold;
}
#sidebar #storyAuthor::before {
  content: "by ";
}
#sidebar #storyAuthor {
  font-size:medium;
  display:block;
  font-weight:bold !important;
}
#sidebar #credits {
  display:block;
  font-size: smaller;
  padding: inherit;
}
#snapbackMenu::before {
  content: "Rewind to:";
  font-weight:bold;
}
#shareMenu::before {
  content: "Share this story at:";
  font-weight:bold;
}
.menu::before {
  content: "Rewind to:";
  font-weight:bold;
}
.menu, .menu div:hover {
  position: static;
  background-color:inherit;
  color:inherit;
  opacity:1;
  border:0;
  font:inherit;
  line-height:inherit;
}
.menu div {
  margin: 0 1.12rem;
  display: list-item;
  list-style:disc outside;
}

"Porthole"
Features: Very roughly inspired by the title screen of "The Sea Will Claim Everything"; Designed for games with brief passage text. No sidebar.

body {
  width: 100%;
  margin-left: 0;
  text-align:center;
}
#passages {
  position:relative;
  display:inline-block;
  font-size: 1.5em;
  background-color:skyblue;
  background-image: -webkit-linear-gradient(top, #87ceeb 0%,#87ceeb 75%,#008eed 75%,#008eed 100%);
  background-image: linear-gradient(to bottom, #87ceeb 0%,#87ceeb 75%,#008eed 75%,#008eed 100%);
  width: 60em;
  height: 60em;
  border-radius: 30em;
  border: darkgoldenrod 1em solid;
  margin-left: 0;
  padding-left: 0;
}
.passage {
  position: absolute;
 text-align:center;
  top: 20em;
  bottom: 0;
  margin: -10em 5em auto 5em;
  display:inline-block;
  width: 40em;
  height: 40em;
  overflow-y: hidden;
  box-shadow: 0 0 2.5em 2.5em;
}
a.internalLink, a.externalLink {
  color: white;
  font-size: 1.2em;
}
a.internalLink:hover, a.externalLink:hover {
  color: white;
  text-decoration: none;
  text-shadow: 0 0 0.5em white;
}
.passage .body {
  color: white;
}
#sidebar {
  display:none;
}
@media screen and (max-width: 960px) {
  body { font-size: 55%; }
}
@media screen and (max-width: 840px) {
  body { font-size: 45%; }
}
@media screen and (max-width: 720px) {
  body { font-size: 40%; }
}

"The Earth's Story 1.0"
Features: No sidebar. Similar to ZX Spectwine, below. Reminiscent of early 90s Nintendo RPGs - hence its gray sensibilities. Use Tag CSS and tag your passages "mint", "strawberry", "banana" or "peanut" to get different coloured borders for specific passages!

body {
  margin: 0;
  background-color:#000;
}
#passages {
  margin: 0;
  padding: 0;
  border: 0;
}
.passage {
  width: 40%;
  min-width: 26em;
  height: 33%;
  min-height: 33%;
  font-family: Helvetica, "Helvetica Neue", Arial, sans-serif;
  letter-spacing: 0.1em;
  padding: 1.5em;
  padding-left: 2em;
  font-size:1.8em;
  background-color:#000;
  color:#eee;
  margin: 10%;
  border: silver ridge 0.8em;
  border-radius: 1em;
}
.passage[data-tags~=mint] {
  border-color: MediumAquaMarine;
}
.passage[data-tags~=strawberry] {
  border-color: HotPink;
}
.passage[data-tags~=banana] {
  border-color: Gold;
}
.passage[data-tags~=peanut] {
  border-color: Peru;
}
.content::before {
  content: '•';
  position: relative;
  left: -0.6em;
  margin-right: -0.4em;
}
a.internalLink, a.externalLink {
  border-bottom: solid #fff 1px;
  color:#eee;
  font-weight:normal;
}
a.internalLink:hover, a.externalLink:hover {
  text-decoration:none;
  border-bottom: solid #fff 2px;
  color:#fff;
  font-weight:normal;
  padding-left: 0;
}
a.internalLink:active, a.externalLink:active {
  border-bottom: 0;
}
#sidebar {
  display:none;
}

"Hypercane 1.1"
As used in Myriad
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 Neue", 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, #sidebar li br {
  display:none !important;
}

"Closed In"
As used in Solitary
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"
As used in To my Grandma
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:hsla(48, 100%, 50%, 0.5);
}
a.externalLink {
  color:#602;
  background-color:hsla(320, 100%, 50%, 0.5);
}
a.internalLink:hover {
  color:#410;
  background-color:hsla(40, 100%, 50%, 0.85);
  text-decoration: none;
}
a.externalLink:hover {
  color:#401;
  background-color:hsla(320, 100%, 50%, 0.85);
  text-decoration: none;
}
a.internalLink:active {
  color:#140;
  background-color:hsla(80, 100%, 50%, 0.85);
  text-decoration: none;
}
a.externalLink:active {
  color:#104;
  background-color:hsla(280, 100%, 50%, 0.85);
  text-decoration: none;
}
#sidebar {
  display:none;
}

"Warm Cabin"
Features: no sidebar; denotes a vague memory of varnished wood as approximated by the MS PowerPoint designers.

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;
}

_{Feel free to report any bugs to @webbedspace.}