feat: add code block copy feature

source/css/layout/common/codeblock/copy-code.styl

@@ -0,0 +1,74 @@
+disable-user-select() {
+  -moz-user-select: none;
+  -ms-user-select: none;
+  -webkit-user-select: none;
+  user-select: none;
+}
+
+.highlight-container {
+  position: relative;
+}
+
+.highlight-container:hover .copy-btn, .highlight-container .copy-btn:focus {
+  opacity: 1;
+}
+
+.copy-btn {
+  color: #333;
+  cursor: pointer;
+  display: inline-block;
+  font-weight: bold;
+  line-height: 1.6;
+  opacity: 0;
+  outline: 0;
+  padding: 2px 6px;
+  position: absolute;
+  vertical-align: middle;
+  white-space: nowrap;
+  disable-user-select();
+  the-transition();
+
+  if (hexo-config('codeblock.style') == 'flat') {
+    background: white;
+    border: 0;
+    font-size: 0.8em;
+    right: 0;
+    top: 0;
+  } else if (hexo-config('codeblock.style') == 'mac') {
+    color: white;
+    font-size: 1em;
+    right: 2px;
+    top: 2px;
+  } else {
+    background-color: #eee;
+    background-image: linear-gradient(#fcfcfc, #eee);
+    border: 1px solid #d5d5d5;
+    border-radius: 3px;
+    font-size: 0.8em;
+    right: 6px;
+    top: 6px;
+  }
+}
+
+
+if (hexo-config('codeblock.style') == 'mac') {
+  .highlight-container {
+    background: #21252b;
+    border-radius: 5px;
+    box-shadow: 0 10px 30px 0 rgba(0, 0, 0, .4);
+    padding-top: 20px;
+    margin-top: 10px;
+
+    &::before {
+      background: #fc625d;
+      border-radius: 50%;
+      box-shadow: 20px 0 #fdbc40, 40px 0 #35cd4b;
+      content: ' ';
+      height: 12px;
+      left: 12px;
+      margin-top: -10px;
+      position: absolute;
+      width: 12px;
+    }
+  }
+}