Basic styling borrowed from _s, with media queries to boot

public/css/main.css

+/*
+CSS reset/normalization taken from _s
+
+_s is based on Underscores http://underscores.me/, (C) 2012-2016 Automattic, Inc.
+Underscores is distributed under the terms of the GNU GPL v2 or later.
+
+Normalizing styles have been helped along thanks to the fine work of
+Nicolas Gallagher and Jonathan Neal http://necolas.github.io/normalize.css/
+*/
+
+/*--------------------------------------------------------------
+# Normalize
+--------------------------------------------------------------*/
+html {
+    font-family: sans-serif;
+    -webkit-text-size-adjust: 100%;
+    -ms-text-size-adjust:     100%;
+}
+
+body {
+    margin: 0;
+}
+
+article,
+aside,
+details,
+figcaption,
+figure,
+footer,
+header,
+main,
+menu,
+nav,
+section,
+summary {
+    display: block;
+}
+
+audio,
+canvas,
+progress,
+video {
+    display: inline-block;
+    vertical-align: baseline;
+}
+
+audio:not([controls]) {
+    display: none;
+    height: 0;
+}
+
+[hidden],
+template {
+    display: none;
+}
+
+a {
+    background-color: transparent;
+}
+
+a:active,
+a:hover {
+    outline: 0;
+}
+
+abbr[title] {
+    border-bottom: 1px dotted;
+}
+
+b,
+strong {
+    font-weight: bold;
+}
+
+dfn {
+    font-style: italic;
+}
+
+h1 {
+    font-size: 2em;
+    margin: 0.67em 0;
+}
+
+mark {
+    background: #ff0;
+    color: #000;
+}
+
+small {
+    font-size: 80%;
+}
+
+sub,
+sup {
+    font-size: 75%;
+    line-height: 0;
+    position: relative;
+    vertical-align: baseline;
+}
+
+sup {
+    top: -0.5em;
+}
+
+sub {
+    bottom: -0.25em;
+}
+
+img {
+    border: 0;
+}
+
+svg:not(:root) {
+    overflow: hidden;
+}
+
+figure {
+    margin: 1em 40px;
+}
+
+hr {
+    box-sizing: content-box;
+    height: 0;
+}
+
+pre {
+    overflow: auto;
+}
+
+code,
+kbd,
+pre,
+samp {
+    font-family: monospace, monospace;
+    font-size: 1em;
+}
+
+button,
+input,
+optgroup,
+select,
+textarea {
+    color: inherit;
+    font: inherit;
+    margin: 0;
+}
+
+button {
+    overflow: visible;
+}
+
+button,
+select {
+    text-transform: none;
+}
+
+button,
+html input[type="button"],
+input[type="reset"],
+input[type="submit"] {
+    -webkit-appearance: button;
+    cursor: pointer;
+}
+
+button[disabled],
+html input[disabled] {
+    cursor: default;
+}
+
+button::-moz-focus-inner,
+input::-moz-focus-inner {
+    border: 0;
+    padding: 0;
+}
+
+input {
+    line-height: normal;
+}
+
+input[type="checkbox"],
+input[type="radio"] {
+    box-sizing: border-box;
+    padding: 0;
+}
+
+input[type="number"]::-webkit-inner-spin-button,
+input[type="number"]::-webkit-outer-spin-button {
+    height: auto;
+}
+
+input[type="search"]::-webkit-search-cancel-button,
+input[type="search"]::-webkit-search-decoration {
+    -webkit-appearance: none;
+}
+
+fieldset {
+    border: 1px solid #c0c0c0;
+    margin: 0 2px;
+    padding: 0.35em 0.625em 0.75em;
+}
+
+legend {
+    border: 0;
+    padding: 0;
+}
+
+textarea {
+    overflow: auto;
+}
+
+optgroup {
+    font-weight: bold;
+}
+
+table {
+    border-collapse: collapse;
+    border-spacing: 0;
+}
+
+td,
+th {
+    padding: 0;
+}
+
+/*--------------------------------------------------------------
+# Typography
+--------------------------------------------------------------*/
+body,
+button,
+input,
+select,
+textarea {
+    color: #404040;
+    font-family: sans-serif;
+    font-size: 16px;
+    font-size: 1rem;
+    line-height: 1.5;
+}
+
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+    clear: both;
+}
+
+p {
+    margin-bottom: 1.5em;
+}
+
+dfn,
+cite,
+em,
+i {
+    font-style: italic;
+}
+
+blockquote {
+    margin: 0 1.5em;
+}
+
+address {
+    margin: 0 0 1.5em;
+}
+
+pre {
+    background: #eee;
+    font-family: "Courier 10 Pitch", Courier, monospace;
+    font-size: 15px;
+    font-size: 0.9375rem;
+    line-height: 1.6;
+    margin-bottom: 1.6em;
+    max-width: 100%;
+    overflow: auto;
+    padding: 1.6em;
+}
+
+code,
+kbd,
+tt,
+var {
+    font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;
+    font-size: 15px;
+    font-size: 0.9375rem;
+}
+
+abbr,
+acronym {
+    border-bottom: 1px dotted #666;
+    cursor: help;
+}
+
+mark,
+ins {
+    background: #fff9c0;
+    text-decoration: none;
+}
+
+big {
+    font-size: 125%;
+}
+
+/*--------------------------------------------------------------
+# Elements
+--------------------------------------------------------------*/
+html {
+    box-sizing: border-box;
+}
+
+*,
+*:before,
+*:after { /* Inherit box-sizing to make it easier to change the property for components that leverage other behavior; see http://css-tricks.com/inheriting-box-sizing-probably-slightly-better-best-practice/ */
+    box-sizing: inherit;
+}
+
+body {
+    background: #fff; /* Fallback for when there is no custom background color defined. */
+}
+
+blockquote:before,
+blockquote:after,
+q:before,
+q:after {
+    content: "";
+}
+
+blockquote,
+q {
+    quotes: "" "";
+}
+
+hr {
+    background-color: #ccc;
+    border: 0;
+    height: 1px;
+    margin-bottom: 1.5em;
+}
+
+ul,
+ol {
+    margin: 0 0 1.5em 3em;
+}
+
+ul {
+    list-style: disc;
+}
+
+ol {
+    list-style: decimal;
+}
+
+li > ul,
+li > ol {
+    margin-bottom: 0;
+    margin-left: 1.5em;
+}
+
+dt {
+    font-weight: bold;
+}
+
+dd {
+    margin: 0 1.5em 1.5em;
+}
+
+img {
+    height: auto; /* Make sure images are scaled correctly. */
+    max-width: 100%; /* Adhere to container width. */
+}
+
+figure {
+    margin: 1em 0; /* Extra wide images within figure tags don't overflow the content area. */
+}
+
+table {
+    margin: 0 0 1.5em;
+    width: 100%;
+}
+
+/*--------------------------------------------------------------
+# Forms
+--------------------------------------------------------------*/
+button,
+input[type="button"],
+input[type="reset"],
+input[type="submit"] {
+    border: 1px solid;
+    border-color: #ccc #ccc #bbb;
+    border-radius: 3px;
+    background: #e6e6e6;
+    color: rgba(0, 0, 0, .8);
+    font-size: 12px;
+    font-size: 0.75rem;
+    line-height: 1;
+    padding: .6em 1em .4em;
+}
+
+button:hover,
+input[type="button"]:hover,
+input[type="reset"]:hover,
+input[type="submit"]:hover {
+    border-color: #ccc #bbb #aaa;
+}
+
+button:focus,
+input[type="button"]:focus,
+input[type="reset"]:focus,
+input[type="submit"]:focus,
+button:active,
+input[type="button"]:active,
+input[type="reset"]:active,
+input[type="submit"]:active {
+    border-color: #aaa #bbb #bbb;
+}
+
+input[type="text"],
+input[type="email"],
+input[type="url"],
+input[type="password"],
+input[type="search"],
+input[type="number"],
+input[type="tel"],
+input[type="range"],
+input[type="date"],
+input[type="month"],
+input[type="week"],
+input[type="time"],
+input[type="datetime"],
+input[type="datetime-local"],
+input[type="color"],
+textarea {
+    color: #666;
+    border: 1px solid #ccc;
+    border-radius: 3px;
+    padding: 3px;
+}
+
+select {
+    border: 1px solid #ccc;
+}
+
+input[type="text"]:focus,
+input[type="email"]:focus,
+input[type="url"]:focus,
+input[type="password"]:focus,
+input[type="search"]:focus,
+input[type="number"]:focus,
+input[type="tel"]:focus,
+input[type="range"]:focus,
+input[type="date"]:focus,
+input[type="month"]:focus,
+input[type="week"]:focus,
+input[type="time"]:focus,
+input[type="datetime"]:focus,
+input[type="datetime-local"]:focus,
+input[type="color"]:focus,
+textarea:focus {
+    color: #111;
+}
+
+textarea {
+    width: 100%;
+}
+
+/*--------------------------------------------------------------
+# Navigation
+--------------------------------------------------------------*/
+/*--------------------------------------------------------------
+## Links
+--------------------------------------------------------------*/
+a {
+    color: royalblue;
+}
+
+a:visited {
+    color: purple;
+}
+
+a:hover,
+a:focus,
+a:active {
+    color: midnightblue;
+}
+
+a:focus {
+    outline: thin dotted;
+}
+
+a:hover,
+a:active {
+    outline: 0;
+}
+
+/*--------------------------------------------------------------
+## Menus
+--------------------------------------------------------------*/
+.main-navigation {
+    clear: both;
+    display: block;
+    float: left;
+    width: 100%;
+}
+
+.main-navigation ul {
+    display: none;
+    list-style: none;
+    margin: 0;
+    padding-left: 0;
+}
+
+.main-navigation li {
+    float: left;
+    position: relative;
+}
+
+.main-navigation a {
+    display: block;
+    text-decoration: none;
+}
+
+.main-navigation ul ul {
+    box-shadow: 0 3px 3px rgba(0, 0, 0, 0.2);
+    float: left;
+    position: absolute;
+    top: 1.5em;
+    left: -999em;
+    z-index: 99999;
+}
+
+.main-navigation ul ul ul {
+    left: -999em;
+    top: 0;
+}
+
+.main-navigation ul ul a {
+    width: 200px;
+}
+
+.main-navigation ul ul li {
+
+}
+
+.main-navigation li:hover > a,
+.main-navigation li.focus > a {
+}
+
+.main-navigation ul ul :hover > a,
+.main-navigation ul ul .focus > a {
+}
+
+.main-navigation ul ul a:hover,
+.main-navigation ul ul a.focus {
+}
+
+.main-navigation ul li:hover > ul,
+.main-navigation ul li.focus > ul {
+    left: auto;
+}
+
+.main-navigation ul ul li:hover > ul,
+.main-navigation ul ul li.focus > ul {
+    left: 100%;
+}
+
+.main-navigation .current_page_item > a,
+.main-navigation .current-menu-item > a,
+.main-navigation .current_page_ancestor > a,
+.main-navigation .current-menu-ancestor > a {
+}
+
+/* Small menu. */
+.menu-toggle,
+.main-navigation.toggled ul {
+    display: block;
+}
+
+@media screen and (min-width: 37.5em) {
+    .menu-toggle {
+        display: none;
+    }
+    .main-navigation ul {
+        display: block;
+    }
+}
+
+.site-main .comment-navigation,
+.site-main .posts-navigation,
+.site-main .post-navigation {
+    margin: 0 0 1.5em;
+    overflow: hidden;
+}
+
+.comment-navigation .nav-previous,
+.posts-navigation .nav-previous,
+.post-navigation .nav-previous {
+    float: left;
+    width: 50%;
+}
+
+.comment-navigation .nav-next,
+.posts-navigation .nav-next,
+.post-navigation .nav-next {
+    float: right;
+    text-align: right;
+    width: 50%;
+}
+
+/*--------------------------------------------------------------
+# Accessibility
+--------------------------------------------------------------*/
+/* Text meant only for screen readers. */
+.screen-reader-text {
+    clip: rect(1px, 1px, 1px, 1px);
+    position: absolute !important;
+    height: 1px;
+    width: 1px;
+    overflow: hidden;
+    word-wrap: normal !important; /* Many screen reader and browser combinations announce broken words as they would appear visually. */
+}
+
+.screen-reader-text:focus {
+    background-color: #f1f1f1;
+    border-radius: 3px;
+    box-shadow: 0 0 2px 2px rgba(0, 0, 0, 0.6);
+    clip: auto !important;
+    color: #21759b;
+    display: block;
+    font-size: 14px;
+    font-size: 0.875rem;
+    font-weight: bold;
+    height: auto;
+    left: 5px;
+    line-height: normal;
+    padding: 15px 23px 14px;
+    text-decoration: none;
+    top: 5px;
+    width: auto;
+    z-index: 100000; /* Above WP toolbar. */
+}
+