A Website Basics
If we were only allowed to give one single most useful tip about web development, it would be: use the “Developer Tools” of your web browser. Most modern web browsers provide these tools. For example, you can find these tools from the menu of Google Chrome
View -> Developer, Firefox’s menu
Tools -> Web Developer, or Safari’s menu
Develop -> Show Web Inspector. Figure A.1 is a screenshot of using the Developer Tools in Chrome.
Typically you can also open the Developer Tools by right-clicking on a certain element on the web page and selecting the menu item
Inspect Element). In Figure A.1, I right-clicked on the profile image of my website https://yihui.name and inspected it, and Chrome highlighted its HTML source code
<img src="..." ... /> in the left pane. You can also see the CSS styles associated with this
img element in the right pane. What is more, you can interactively change the styles there if you know CSS, and see the (temporary) effects in real time on the page! After you are satisfied with the new styles, you can write the CSS code in files.