remove height: 100% from html+body

This prevented a full-sized body, so all content overflew.
Dark themes should be working now :)

_sass/sassline-base/_reset.scss

@@ -5,7 +5,6 @@
 * { box-sizing: border-box; }
 html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, dl, dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td, article, aside, canvas, details, embed, figure, figcaption, footer, header, hgroup, menu, nav, output, ruby, section, summary, time, mark, audio, video { margin: 0; padding: 0; border: 0; font-size: 100%; font: inherit; vertical-align: baseline; }
 article, aside, details, figcaption, footer, header, hgroup, menu, nav, section { display: block; }
-html, body { height: 100%; }
 a img { border: none; }
 blockquote { quotes: none; }
 blockquote:before, blockquote:after { content: ''; content: none; }

assets/styles.scss

@@ -15,7 +15,6 @@ title: false
 body {
   background: $backgroundColour;
   color: $bodyColour;
-  height: 100%;
   display: flex;
   @include flex-direction(column);
   overflow-x: hidden;