Creating Multiple Selection Drop-Downs Based on Previous Selection
For example, lets say a user has to choose a "product category" and a "product subcategory". If a user chooses "shoes" from the first drop down menu, a second drop-down menu automatically appears with choices like "nike, adidas, puma".
To further this example, lets say the user chose "computers" instead of "bedding." Then the second-drop down menu would have choices like "sony, dell, apple".
Following the third-drop down menu would have options based upon the second-drop menu. For example, after selecting apple, the drop-down menu will show "MacBook Air, MacBook Pro, iMac"
How would one go about doing something like that? Is it something you would do in HTML/CSS or some other form?
Thanks for the help!
Note: I have some of the coding for when you have just two drop down menus, but how do you add another drop down menu to have in total 3 drop-down menus.
Here is the code that I have so far but need more help: