Feature: Incorporate site search into masthead (#1383)

* Integrate search into masthead
* Fix cutoff descenders in archive article titles
* Remove search page from `/test` site
* Enable masthead search
* Remove dedicated search page
* Fix masthead search form padding
* Improve insertion of search content
* Speed up page transition
* Add fade transition to search content
* Rename visibility class names
* Add `site.search` to _config.yml
* Document site search feature
* Update CHANGELOG and history

_sass/minimal-mistakes/_base.scss

@@ -21,7 +21,12 @@ body {
   }
 }
 
-h1, h2, h3, h4, h5, h6 {
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
   margin: 2em 0 0.5em;
   line-height: 1.2;
   font-family: $header-font-family;
@@ -53,7 +58,8 @@ h6 {
   font-size: $type-size-6;
 }
 
-small, .small {
+small,
+.small {
   font-size: $type-size-6;
 }
 
@@ -76,7 +82,15 @@ del a {
 
 /* reduce orphans and widows when printing */
 
-p, pre, blockquote, ul, ol, dl, figure, table, fieldset {
+p,
+pre,
+blockquote,
+ul,
+ol,
+dl,
+figure,
+table,
+fieldset {
   orphans: 3;
   widows: 3;
 }
@@ -127,9 +141,19 @@ a {
   }
 }
 
+/* buttons */
+
+button:focus {
+  @extend %tab-focus;
+}
+
 /* code */
 
-tt, code, kbd, samp, pre {
+tt,
+code,
+kbd,
+samp,
+pre {
   font-family: $monospace;
 }
 
@@ -150,7 +174,8 @@ td > code {
   border-radius: $border-radius;
   box-shadow: $box-shadow;
 
-  &:before, &:after {
+  &:before,
+  &:after {
     letter-spacing: -0.2em;
     content: "\00a0"; /* non-breaking space*/
   }
@@ -187,9 +212,9 @@ figure {
   display: -webkit-box;
   display: flex;
   -webkit-box-pack: justify;
-          justify-content: space-between;
+  justify-content: space-between;
   -webkit-box-align: start;
-          align-items: flex-start;
+  align-items: flex-start;
   flex-wrap: wrap;
   margin: 2em 0;
 
@@ -255,14 +280,12 @@ figcaption {
   }
 }
 
-
 /* Fix IE9 SVG bug */
 
 svg:not(:root) {
   overflow: hidden;
 }
 
-
 /*
    Navigation lists
    ========================================================================== */
@@ -310,7 +333,28 @@ nav {
    Global animation transition
    ========================================================================== */
 
-b, i, strong, em, blockquote, p, q, span, figure, img, h1, h2, header, input, a, tr, td, form button, input[type="submit"], .btn, .highlight, .archive__item-teaser {
+b,
+i,
+strong,
+em,
+blockquote,
+p,
+q,
+span,
+figure,
+img,
+h1,
+h2,
+header,
+input,
+a,
+tr,
+td,
+form button,
+input[type="submit"],
+.btn,
+.highlight,
+.archive__item-teaser {
   -webkit-transition: $global-transition;
   transition: $global-transition;
-}
+}