Changes on top of Sleek theme. I've only styled for things I've seen up to something like year 800 but I wanted something a little cleaner.

kitten-game-styles.css

#calendarSign {
    font-size: 22px;
}

#devPanel {
    display: none;
}

#gameLog {
    font-size: 10px;
}

#gameLog > span.msg {
    display: block;
    line-height: 1em;
    margin: 1px 0;
}

#gameLog > span.msg.type_date {
    display: block;
    height: 16px;
    line-height: 1.5em;
    margin-bottom: 3px;
    margin-top: 10px;
}

#gameLog > span.msg.type_date:before {
    content: '';
}

#gameLog > span.msg.type_date:first-child {
    margin-top: 0;
}

#gameLog > span.msg:before {
    color: #78809b;
    content: '• ';
}

#leftColumn > div:first-child a {
    padding-left: 0px;
}

#leftColumn > div:first-child a:after {
    content: "–";
    left: 4px;
    position: relative;
}

#leftColumn > div[style="float:right; margin-right:-13px;"] {
    margin-right: 0px;
}

#midColumn {
    margin-top: 3px;
}

#pauseBtn {
    background-color: #C90202;
    border-bottom: 2px solid #6B0000;
    border-radius: 5px;
    color: white;
    display: inline-block;
    font-size: 12px;
    padding: 5px 8px;
    position: absolute;
    right: 15px;
    top: 100px;
}

#rightColumn {
    position: relative;
    top: 55px;
}

.panelContainer table table td:first-child {
    padding-right: 10px;
    text-transform: capitalize;
}

.scheme_sleek .resourceRow > td:first-child {
    padding-left: 0px;
}

.scheme_sleek .resourceRow td {
    font-size: 12px;
    padding: 0 6px;
    padding-bottom: 2px;
    text-shadow: none;
}

.scheme_sleek .resourceRow td.resLimitNotice {
    color: #ab312a;
}

.scheme_sleek .resourceRow td.resLimitNotice::after {
    color: #ab312a;
    display: none;
    text-shadow: none;
}

.scheme_sleek .resourceRow td.resLimitWarn {
    color: #e2ca00;
}

.scheme_sleek .resourceRow td.resLimitWarn::after {
    color: #e2ca00;
    display: none;
    text-shadow: none;
}

.scheme_sleek #footerLinks {
    background-color: #1c1917;
    padding-top: 10px;
}

.scheme_sleek #headerLinks {
    top: 4px ;
}

.scheme_sleek table.craftTable tr:hover td {
    background-color: rgba(204, 204, 204, 0.14);
}

.scheme_sleek td.resAmount {
    color: #3980B1;
}

.scheme_sleek tr.resourceRow:hover {
    background-color: rgba(204, 204, 204, 0.14);
}

.scheme_sleek tr.resourceRow:hover td {
    background-color: rgba(204, 204, 204, 0.14);
}

.tabInner {
    padding-top: 0px;
}

.tabInner > div > a {
    background-color: #333745;
    border-bottom: none;
    border-radius: 3px;
    color: rgb(255, 255, 255);
    display: none;
    font-size: 8px;
    margin: 0 2px;
    padding: 3px 5px;
}

.tabInner > div > a.activeTab {
    background-color: #26374f;
    border-bottom: none;
}

.tabInner > div > a:first-child {
    margin-left: -2px;
}

.tabInner > div > a:hover {
    background-color: #4a4f64;
}

.tabInner > div > span {
    display: none;
}

.tabInner > div > span.achievement {
    display: block;
}

.tabInner > div > span.achievement[title='???'] {
    display: none;
}

a {
    text-shadow: none;
}

a:hover {
    color: rgb(99, 147, 185);
    text-decoration: none;
}

a[title="Make Senator"] {
    visibility: hidden;
}

a[title="Make Senator"]:before {
    content: " Make Senator";
    visibility: visible;
}

a[title="Make a leader"] {
    visibility: hidden;
}

a[title="Make a leader"]:before {
    content: " Make Leader";
    visibility: visible;
}

/* ======= */

/* GENERAL */

/* =========== */

/* ============= */

/* CENTER-COLUMN */

/* ============= */

/* ============ */

/* RIGHT-COLUMN */

/* ============ */

/*.button_tooltip .noRes, .limited {
    color: #CE6363;
}*/

/* ======= */

/*
/scheme_sleek #tooltip {
    position: relative ;
    overflow: hidden ;
    left: 850px;
    display: inline-block;
    bottom: 40px;
}

.scheme_sleek #tooltip .flavor {
    color: #00b7ff;
}

.scheme_sleek #tooltip>div:first-child>div:first-child {
    margin-bottom: 10px !important;
}
*/

/* ====== */

/* HEADER */

/* ====== */

/*.scheme_sleek #topbar {
    height: 21px;
    padding-top: 3px;
}*/

/* =========== */

/* LEFT-COLUMN */

div#resContainer {
    margin-left: 0px;
    padding-top: 25px;
}

div.bldGroupContainer {
    background-color: #171513;
    margin-top: 20px;
    padding: 20px
;
}

div.tabsContainer {
    text-align: center;
}

div.tabsContainer > a.tab {
    background-color: #4a4a4a;
    border-bottom: none;
    border-radius: 2px;
    color: rgba(255, 255, 255, 0.85);
    display: inline-block;
    font-size: 14px;
    margin: 6px 3px;
    padding: 5px 7px;
}

div.tabsContainer > a.tab.activeTab {
    background-color: #26374f;
    color: white;
}

div.tabsContainer > a.tab.activeTab:hover {
    background-color: #374f72;
    color: white;
}

div.tabsContainer > a.tab:hover {
    background-color: #646464;
}

div.tabsContainer > span {
    display: none;
}

div.title + div.container > div > div:nth-child(2n) > a {
    text-align: right;
}

div.title + div.container > div > div:nth-child(2n) > a:before {
    display: inline-block;
    margin-right: -13px;
}

html, body {
    background: linear-gradient(to right, #1c1917 0%, #1c1917 24%, #1c1917 76%, #1c1917 100%);
    font-family: 'arial';
    font-size: 15px;
}

span#calendarDiv {
    font-size: 18px;
}

table {
    border-collapse: collapse;
}

tr.resourceRow td.resource-name, #craftContainer tr.resourceRow > td:first-child {
    color: white;
    font-size: 12px
;
    text-transform: capitalize;
}