clean up shortcodes

assets/sass/components/_embeds.scss

@@ -1,5 +1,5 @@
 // External social embeds
-div.embed {
+.embed {
   &.codepen {
     iframe {
       width: 100%;
@@ -8,8 +8,10 @@ div.embed {
   }
 
   &.tweet {
-    .twitter-tweet-rendered iframe {
-      margin: 0.5em 0;
+    margin: 0.5em 0;
+
+    > .twitter-tweet-rendered {
+      margin: 0 auto;
     }
   }
 
@@ -40,12 +42,25 @@ div.embed {
     }
   }
 
+  &.vimeo {
+    padding: 75% 0 0 0;
+    position: relative;
+
+    iframe {
+      position: absolute;
+      top: 0;
+      left: 0;
+      width: 100%;
+      height: 100%;
+    }
+  }
+
   &.gh-buttons {
     text-align: center;
 
     // GitHub's script replaces <a> with <span>, so cover both
-    > span,
-    > a {
+    > a,
+    > span {
       margin: 0 0.5em;
     }
   }