docs(pages): 为 Astro 加上在新标签页打开链接的功能

2. del(music): 删除音乐：在银河中孤独摇摆
3. fix(config): 简单修复即使 background 为关闭时依然加载背景图片的问题
4. chore(friends): 加入新的友链
5. style(friends): 优化友情链接页面的样式
6. style(footer): 修改 footer 页脚文本
7. fix(css): 修复复制按钮无法显示的问题

src/styles/markdown.css

@@ -1,3 +1,18 @@
+.btn-regular-dark {
+    @apply bg-gray-800 text-white;
+  }
+  
+  .btn-regular-bg {
+    @apply bg-gray-100 dark:bg-gray-800;
+  }
+  
+  .btn-plain-bg-hover {
+    @apply bg-gray-50 dark:bg-gray-700;
+  }
+  
+  .btn-plain-bg-active {
+    @apply bg-gray-200 dark:bg-gray-600;
+  }
 .custom-md {
     h1 {
         @apply text-3xl;
@@ -19,7 +34,6 @@
         }
     }
 
-    /* https://github.com/afoim/fuwari/blob/main/src/styles/markdown.css */
     a:not(.no-styling) {
         @apply relative bg-none transition rounded-md p-1 -m-1 font-medium text-[var(--primary)]
         before:ease-out before:transition active:bg-none hover:before:bg-[var(--btn-plain-bg-hover)] active:before:bg-[var(--btn-plain-bg-active)] z-0
@@ -61,10 +75,30 @@
         }
     }
 
+    .copy-btn {
+        all: initial;
+        @apply btn-regular-dark opacity-0 shadow-lg shadow-black/50 absolute active:scale-90 h-8 w-8 top-3 right-3 text-sm rounded-lg transition-all ease-in-out z-20 cursor-pointer;
+    }
     .frame:hover .copy-btn {
         opacity: 1;
     }
 
+    .copy-btn-icon {
+        @apply absolute top-1/2 left-1/2 transition -translate-x-1/2 -translate-y-1/2 w-4 h-4 fill-white pointer-events-none;
+    }
+    .copy-btn .copy-icon {
+        @apply opacity-100 fill-white dark:fill-white/75;
+    }
+    .copy-btn.success .copy-icon {
+        @apply opacity-0 fill-[var(--deep-text)]
+    }
+    .copy-btn .success-icon {
+        @apply opacity-0 fill-white;
+    }
+    .copy-btn.success .success-icon {
+        @apply opacity-100
+    }
+
     .expressive-code {
         @apply my-4;
         ::selection {
@@ -72,7 +106,6 @@
         }
     }
 
-
     ul, ol {
         li::marker {
             @apply text-[var(--primary)];
@@ -93,11 +126,4 @@
         }
 
     }
-
-    .katex-display-container {
-        max-width: 100%;
-        overflow-x: auto;
-        margin: 1em 0;
-    }
-    
 }