feat: Demo updates

I guess it's ready to be shown to Masto folks!

_sass/custom.scss

@@ -1,4 +1,6 @@
 /* Custom styles/overrides */
+
+/* Fix contrast of OP badge/instance in comments (remove if color with higher contrast are used as accent) */
 section#comments {
   .comment {
     .avatar-link {

_sass/main.scss

@@ -179,6 +179,15 @@ kbd:active {
   filter: contrast(0.2);
 }
 
+figcaption {
+  margin-top: -1rem;
+  margin-bottom: 2rem;
+  display: block;
+  text-align: center;
+  color: var(--fg50);
+  font-size: smaller;
+}
+
 /* Tables */
 table {
   border-collapse: collapse;
@@ -235,6 +244,15 @@ video {
   max-width: 100%;
 }
 
+video.full {
+  width: 100%;
+}
+
+video.pixels {
+  image-rendering: crisp-edges; /* older firefox browsers */
+  image-rendering: pixelated;
+}
+
 .media {
   border-radius: var(--border-radius-small);
   box-shadow: var(--shadow);