Add audio and video shortcodes with basic controls; enhance CSS for media elements

assets/css/common/post-single.css

@@ -415,3 +415,19 @@ img.in-text {
     display: inline;
     margin: auto;
 }
+
+mark {
+    border-radius: 2px;
+    padding: 0 2px;
+}
+
+audio {
+    width: stretch;
+    max-width: 100%;
+}
+
+video {
+    border: 1px solid var(--code-bg);
+    border-radius: var(--radius);
+    max-width: 100%;
+}

layouts/shortcodes/audio.html

@@ -0,0 +1,2 @@
+{{ $src := (.Get "src") }}
+<audio src="{{ $src }}" controls muted></audio>

layouts/shortcodes/video.html

@@ -0,0 +1,2 @@
+{{ $src := (.Get "src") }}
+<video src="{{ $src }}" controls muted></video>