diff --git a/apps/test/content/posts/code-tabs-test.md b/apps/test/content/posts/code-tabs-test.md
index 8f3c1e7a..943ed2ee 100644
--- a/apps/test/content/posts/code-tabs-test.md
+++ b/apps/test/content/posts/code-tabs-test.md
@@ -40,6 +40,19 @@ def sum(a, b):
 print(sum(1, 2))
 ```
 
+## Active Tab
+
+```js {group=tab-active name="Inactive Tab"}
+function greet(name) {
+  return `Hello, ${name}!`
+}
+```
+
+```python {group=tab-active name="Active Tab" .active}
+def greet(name):
+  return f"Hello, {name}!"
+```
+
 ## Mode
 
 ```ts {group=tab-mode name="Classic"}
diff --git a/assets/css/_page/_single/_code.scss b/assets/css/_page/_single/_code.scss
index 0cf9b10f..853a18f4 100644
--- a/assets/css/_page/_single/_code.scss
+++ b/assets/css/_page/_single/_code.scss
@@ -590,27 +590,40 @@ pre {
     .tabs-items {
       display: flex;
       overflow-x: auto;
+      position: relative;
       @include border-radius(top);
-      
+
       .tab-item {
         padding: 0.4rem 0.8rem;
         cursor: pointer;
         font-weight: bold;
         color: fixit-var(secondary);
         white-space: nowrap;
-        transition: all 0.2s;
         user-select: none;
-        
-        &:hover {
-          color: fixit-var(global-font-color);
-          background-color: rgba(128, 128, 128, 0.05);
-        }
-        
-        &.active {
-          color: fixit-var(global-font-color);
-          box-shadow: inset 0 -2px 0 fixit-var(code-tab-active-border-color, fixit-var(primary));
-          background-color: fixit-var(code-block-background-color);
-        }
+        @include border-radius;
+
+        // mobile style
+        // padding-inline: 0.6rem;
+      }
+
+      &:not(:has(.tab-item:hover)) .tab-item.active,
+      .tab-item:hover {
+        anchor-name: #{$rootPrefix}tab-hover;
+        color: fixit-var(global-font-color);
+      }
+
+      &::before {
+        content: '';
+        position-anchor: #{$rootPrefix}tab-hover;
+        position: absolute;
+        inset: anchor(inside);
+        translate: 2px 2px;
+        width: calc(anchor-size(width) - 0.25rem);
+        height: calc(anchor-size(height) - 0.25rem);
+        box-shadow: inset 0 0 1rem 0.25rem color-mix(in srgb, fixit-var(secondary) 30%, transparent);
+        pointer-events: none;
+        transition: 0.3s ease-in-out;
+        @include border-radius;
       }
     }
 
diff --git a/assets/css/_page/_single/_shortcodes/_tabs.scss b/assets/css/_page/_single/_shortcodes/_tabs.scss
index 1a916e8f..00c1a928 100644
--- a/assets/css/_page/_single/_shortcodes/_tabs.scss
+++ b/assets/css/_page/_single/_shortcodes/_tabs.scss
@@ -107,17 +107,15 @@ tab-container {
 
   // ========================================
   // Style 1: Underline Style (Default)
-  // Clean, minimal with bottom border
+  // Clean, minimal with sliding indicator
   // ========================================
   &[type='underline'] {
     > .tab-button {
-      @include set-fixit-var(tab-button-border-color, transparent);
       @include tab-button-size(0);
 
       &[aria-selected='true'],
       &[aria-selected='false']:hover {
         color: fixit-var(primary);
-        @include set-fixit-var(tab-button-border-color, fixit-var(primary));
       }
 
       &[aria-selected='false']:hover {
@@ -125,6 +123,21 @@ tab-container {
       }
     }
 
+    // Anchor tracking: follows hover, rests on active tab
+    &:not(:has(> .tab-button:hover)) > .tab-button[aria-selected='true'],
+    > .tab-button:hover {
+      anchor-name: #{$rootPrefix}tab-underline-active;
+    }
+
+    // Sliding box-shadow indicator via anchor positioning
+    &::part(tablist-tab-wrapper)::before {
+      content: '';
+      position: absolute;
+      position-anchor: #{$rootPrefix}tab-underline-active;
+      inset: anchor(inside);
+      pointer-events: none;
+    }
+
     &[placement='top'],
     &[placement='bottom'] {
       gap: 0.5rem;
@@ -137,6 +150,10 @@ tab-container {
         overflow-x: scroll;
         overflow-y: hidden;
       }
+
+      &::part(tablist-tab-wrapper)::before {
+        transition: all 0.3s ease-in-out, top, bottom 0s;
+      }
     }
 
     &[placement='left'],
@@ -144,17 +161,21 @@ tab-container {
       > .tab-button {
         @include tab-button-size(1rem, 0);
       }
+
+      &::part(tablist-tab-wrapper)::before {
+        transition: all 0.3s ease-in-out, left, right 0s;
+      }
     }
 
     // Top placement
     &[placement='top'] {
       &::part(tablist-tab-wrapper) {
         border-bottom: 2px solid fixit-var(global-border-color);
-      }
 
-      > .tab-button {
-        translate: 0 2px;
-        border-bottom: 2px solid fixit-var(tab-button-border-color);
+        &::before {
+          box-shadow: inset 0 -2px 0 fixit-var(primary);
+          translate: 0 2px;
+        }
       }
     }
 
@@ -162,11 +183,11 @@ tab-container {
     &[placement='bottom'] {
       &::part(tablist-tab-wrapper) {
         border-top: 2px solid fixit-var(global-border-color);
-      }
 
-      > .tab-button {
-        translate: 0 -2px;
-        border-top: 2px solid fixit-var(tab-button-border-color);
+         &::before {
+          box-shadow: inset 0 2px 0 fixit-var(primary);
+          translate: 0 -2px;
+        }
       }
     }
 
@@ -174,12 +195,15 @@ tab-container {
     &[placement='left'] {
       &::part(tablist-tab-wrapper) {
         border-right: 2px solid fixit-var(global-border-color);
+
+        &::before {
+          box-shadow: inset -2px 0 0 fixit-var(primary);
+          translate: 2px 0;
+        }
       }
 
       > .tab-button {
         text-align: right;
-        translate: 2px 0;
-        border-right: 2px solid fixit-var(tab-button-border-color);
       }
     }
 
@@ -187,12 +211,15 @@ tab-container {
     &[placement='right'] {
       &::part(tablist-tab-wrapper) {
         border-left: 2px solid fixit-var(global-border-color);
+
+        &::before {
+          box-shadow: inset 2px 0 0 fixit-var(primary);
+          translate: -2px 0;
+        }
       }
 
       > .tab-button {
         text-align: left;
-        translate: -2px 0;
-        border-left: 2px solid fixit-var(tab-button-border-color);
       }
     }
   }
@@ -451,8 +478,10 @@ tab-container {
     }
 
     > .tab-button {
+      position: relative;
       font-weight: 400;
       flex-grow: 1;
+      @include z-index(base);
 
       @include tab-button-size;
       @include border-radius;
@@ -463,12 +492,26 @@ tab-container {
       }
 
       &[aria-selected='true'] {
-        background-color: fixit-var(global-background-color);
-        box-shadow: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.1);
+        anchor-name: #{$rootPrefix}tab-segment-active;
+        background-color: transparent;
+        box-shadow: none;
+      }
+    }
 
-        [data-theme=dark] & {
-          box-shadow: 0 0.125rem 0.25rem rgba(255, 255, 255, 0.1);
-        }
+    // Sliding active indicator via anchor positioning
+    &::part(tablist-tab-wrapper)::before {
+      content: '';
+      position: absolute;
+      pointer-events: none;
+      position-anchor: #{$rootPrefix}tab-segment-active;
+      inset: anchor(inside);
+      background-color: fixit-var(global-background-color);
+      box-shadow: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.1);
+      transition: all 0.15s ease, top, bottom 0s;
+      @include border-radius;
+
+      [data-theme=dark] & {
+        box-shadow: 0 0.125rem 0.25rem rgba(255, 255, 255, 0.1);
       }
     }
   }
@@ -531,3 +574,54 @@ tab-container {
 tab-container .tab-panel:not([hidden]) {
   animation: tabSlideIn 0.3s ease-out;
 }
+
+// Firefox fallback: `::part(...)::before` is not supported.
+// We use a CSS variable to control the border color of the active tab button,
+// and apply the sliding effect directly on the button itself.
+@supports (-moz-appearance: none) {
+  tab-container {
+    &[type='underline'] {
+      > .tab-button {
+        @include set-fixit-var(tab-button-border-color, transparent);
+
+        &[aria-selected='true'],
+        &[aria-selected='false']:hover {
+          @include set-fixit-var(tab-button-border-color, fixit-var(primary));
+        }
+      }
+
+      &[placement='top'] > .tab-button {
+        translate: 0 2px;
+        border-bottom: 2px solid fixit-var(tab-button-border-color);
+      }
+
+      &[placement='bottom'] > .tab-button {
+        translate: 0 -2px;
+        border-top: 2px solid fixit-var(tab-button-border-color);
+      }
+
+      &[placement='left'] > .tab-button {
+        translate: 2px 0;
+        border-right: 2px solid fixit-var(tab-button-border-color);
+      }
+
+      &[placement='right'] > .tab-button {
+        translate: -2px 0;
+        border-left: 2px solid fixit-var(tab-button-border-color);
+      }
+    }
+
+    &[type='segment'] {
+      > .tab-button {
+        &[aria-selected='true'] {
+          background-color: fixit-var(global-background-color);
+          box-shadow: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.1);
+
+          [data-theme=dark] & {
+            box-shadow: 0 0.125rem 0.25rem rgba(255, 255, 255, 0.1);
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/assets/js/theme.js b/assets/js/theme.js
index 46c68ceb..6b676e33 100644
--- a/assets/js/theme.js
+++ b/assets/js/theme.js
@@ -640,13 +640,15 @@ class FixIt {
       const $firstBlock = $tabs[0];
       $firstBlock.parentNode.insertBefore($container, $firstBlock);
       
+      const activeTabIndex = $tabs.findIndex(tab => tab.classList.contains('active'));
       $tabs.forEach(($tab, index) => {
         const title = $tab.dataset.tabTitle || 'Code';
+        const defaultActiveTab = activeTabIndex === -1 && index === 0;
         
         // tab button
         const $btn = document.createElement('span');
         $btn.className = 'tab-item';
-        if (index === 0) $btn.classList.add('active');
+        if (defaultActiveTab) $btn.classList.add('active');
         $btn.textContent = title;
         $btn.dataset.index = index;
         $btn.title = title;
@@ -678,8 +680,7 @@ class FixIt {
         $items.appendChild($btn);
         
         // move block to content
-        $tab.classList.toggle('active', index === 0);
-        // remove is-collapsed class
+        $tab.classList.toggle('active', activeTabIndex === index || defaultActiveTab);
         $tab.classList.remove('is-collapsed');
         $content.appendChild($tab);
       });
@@ -687,8 +688,13 @@ class FixIt {
       $container.appendChild($header);
       $container.appendChild($content);
 
-      // initialize actions for first tab
-      $items.firstElementChild.click();
+      // initialize actions for the active tab
+      if (activeTabIndex !== -1) {
+        const $activeBtn = $items.querySelector(`.tab-item[data-index="${activeTabIndex}"]`);
+        if ($activeBtn) $activeBtn.click();
+      } else {
+        $items.firstElementChild.click();
+      }
     });
   }