Web page is based on 12 grid then we can divide 2,3 and 4 column evenly and looks tidy.
Resposive webpage is that the webpage is fit on each device screen size automatically.
The semantic structure is the tags are needing to locate at the correct place in html, for example the body tag is inside of the html tag and the div tag is inside of the body tag.
Bootstrap is very interesting, I am not sure how can I read all their information.
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