visual changes and add thumbnail button for blog - #352

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

'Rvec_sub' is assigned a value but never used

'Bvec_add' is assigned a value but never used