1st

.gitignore

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+/source/logo/*

content.js

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+window.onload = function () {
+    let logo_base = document.querySelector('#logo-icon');
+    let logo_base2 = logo_base.querySelector('.yt-icon');
+    let logo_base3 = logo_base2.querySelector('.yt-spec-icon-shape');
+    let logo_base4 = logo_base3.querySelector('div');
+    let logo_base5 = logo_base4.querySelector('svg');
+    if (logo) {
+        let logo_img = chrome.runtime.getURL('source/logo/YTHUB.png');
+        logo_base5.outerHTML = '<img src="' + logo_img + '" width="90" height="20">'; // ここに置き換えたい画像のURLを指定してください
+    }
+};

manifest.json

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+{
+    "manifest_version": 2,
+    "name": "YouTube Logo Replacer",
+    "version": "1.0",
+    "description": "Replace YouTube logo with a specified image",
+    "content_scripts": [
+      {
+        "matches": ["https://www.youtube.com/*"],
+        "js": ["content.js"]
+      }
+    ],
+    "permissions": ["activeTab", "storage"],
+    "web_accessible_resources": [
+        "source/logo/*"
+    ]
+}

newFile.js

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+// content.js
+window.onload = function() {
+    let logo = document.querySelector('.yt-icon');
+    if (logo) {
+        let logo_img = browser.runtime.getURL('source/logo/self_dlsite.png');
+        logo.outerHTML = '<img src="' + logo_img + '">'; // ここに置き換えたい画像のURLを指定してください
+    }
+  };
+