feat(ui): improve block quote layout

Author: cotes2020

_sass/addon/commons.scss

@@ -80,9 +80,10 @@ img {
 }
 
 blockquote {
-  border-left: 5px solid var(--blockquote-border-color);
+  border-left: 0.125rem solid var(--blockquote-border-color);
   padding-left: 1rem;
   color: var(--blockquote-text-color);
+  margin-top: 0.5rem;
 
   > p:last-child {
     margin-bottom: 0;