I need to increase the width of search box in home page.
With the help of developer tools i have found that block-search (.block-search) class is reason for this and i have checked .block-search in my magento2 directory.
And i have found .block-search class in
\pub\static\frontend\Magento\luma\en_US\css\styles-l.css for which i have changed the size and its working fine.
Now in the future to get updates for any css classes i may delete pub/static files. So how to find the core files reason for any css, so that even i delete pub/static files it won't get effected to my changes requirement