docs: add README logo

Add the selected CSS-Diff logo asset and update both README variants with a centered project header.

Author: jevin98

README.md

@@ -1,8 +1,12 @@
-# CSS-Diff
+<divalign="center">
+ <imgsrc="./img/logo.png"alt="CSS-Diff logo"width="160">
 
-English | [简体中文](./README.zh-CN.md)
+ <h1>CSS-Diff</h1>
 
-CSS-Diff is a DevTools sidebar extension for comparing the computed CSS of two DOM elements. It is built for frontend debugging: select two elements in the Elements panel, then inspect what changed, search for a property, and copy a CSS declaration with one click.
+ <p>English | <ahref="./README.zh-CN.md">简体中文</a></p>
+
+ <p>CSS-Diff is a DevTools sidebar extension for comparing the computed CSS of two DOM elements. It is built for frontend debugging: select two elements in the Elements panel, then inspect what changed, search for a property, and copy a CSS declaration with one click.</p>
+</div>
 
 ![Screenshot](https://github.com/Jevin0/css-diff-devtools/blob/main/img/screenshot.png?raw=true)
 

README.zh-CN.md

@@ -1,8 +1,12 @@
-# CSS-Diff
+<divalign="center">
+ <imgsrc="./img/logo.png"alt="CSS-Diff logo"width="160">
 
-[English](./README.md) | 简体中文
+ <h1>CSS-Diff</h1>
 
-CSS-Diff 是一个用于比较两个 DOM 元素计算后 CSS 的 DevTools 侧边栏扩展。它面向前端调试场景：在 Elements 面板中选择两个元素，即可查看哪些样式发生了变化、搜索指定属性，并一键复制 CSS 声明。
+ <p><ahref="./README.md">English</a> | 简体中文</p>
+
+ <p>CSS-Diff 是一个用于比较两个 DOM 元素计算后 CSS 的 DevTools 侧边栏扩展。它面向前端调试场景：在 Elements 面板中选择两个元素，即可查看哪些样式发生了变化、搜索指定属性，并一键复制 CSS 声明。</p>
+</div>
 
 ![Screenshot](https://github.com/Jevin0/css-diff-devtools/blob/main/img/screenshot.png?raw=true)