fix(#15): Delete the hover effect of the back2top button

layout/_partials/widgets/back2top.pug

 - var fa_prefix = theme.fa_prefix || 'fa'
 
 div#back2top.back2top
-  div(data-popover=__("back2top") data-popover-pos="up")
-    i.back2top-icon(class=`${fa_prefix} fa-${theme.back2top.icon.name}`)
+  i.back2top-icon(class=`${fa_prefix} fa-${theme.back2top.icon.name}`)

source/css/_common/components/widgets/back2top.styl

@@ -26,8 +26,4 @@
       color: convert(hexo-config('back2top.icon.hover_color') || '#999');
     }
   }
-
-  &[data-popover][data-popover-pos='up']:hover::before {
-    transform: translate(-50%, -125%);
-  }
 }

source/css/_common/components/widgets/sticky-top.styl

@@ -18,10 +18,6 @@
     color: convert(hexo-config('stick_top.color' || '#999'));
     transform: scale(1.2) rotate(stick-top-rotate);
   }
-
-  &[data-popover][data-popover-pos='up']:hover::before {
-    transform: translate(-50%, -100%);
-  }
 }
 
 .archive {

source/css/_common/scaffolding/utils.styl

@@ -37,9 +37,11 @@ popover-bg-color = alpha(#000, .7);
   padding: .2rem .6rem;
 }
 
-[data-popover][data-popover-pos='up']:hover::before {
-  opacity: 1;
-  transform: translate(-50%, -115%);
+@media (min-width: $md-width) {
+  [data-popover-pos='up']:hover::before {
+    opacity: 1;
+    transform: translate(-50%, -120%);
+  }
 }
 
 // "Alert" component