refactor(article): add default padding (#166)

* refactor(article): add default padding

closes https://github.com/CaiJimmy/hugo-theme-stack/issues/165

* fix(article): video iframe margin

* fix: remove youtube iframe border

layouts/shortcodes/bilibili.html

@@ -12,13 +12,12 @@
     <p>当前视频av或BV号：{{ $vid }}，视频分P：{{ $videopage }}</p>
 {{ end }}
 
-<div style="position: relative; width: 100%; height: 0; padding-bottom: 56.25%;">
+<div class="video-wrapper">
     <iframe src="//player.bilibili.com/player.html?{{ $basicQuery | safeURL }}&{{ $videoQuery | safeURL }}"
             scrolling="no"
             frameborder="no"
             framespacing="0"
             allowfullscreen="true"
-            style="position: absolute; width: 100%; height: 100%; left: 0; top: 0;"
     >
     </iframe>
 </div>