change del element decoration to line-through (#1181)

According to caniuse.com only around 69% of mobile user and 22% desktop users use a browser that supports this element. Therefore this change uses text-decoration: line-through to archive the same effect across browsers.

assets/css/common/post-single.css

@@ -83,8 +83,7 @@
 }
 
 .post-content del {
-    text-decoration: none;
-    background: linear-gradient(to right, var(--primary) 100%, transparent 0) 0 50%/1px 1px repeat-x;
+    text-decoration: line-through;
 }
 
 .post-content dl,
@@ -400,4 +399,4 @@ h1>a>svg {
 img.in-text {
     display: inline;
     margin: auto;
-}
+}