I was asked about how I did my tag page(s) so I thought I'd do a little tutorial (because I may have always wanted to make one of those^^).
[Disclaimer: The original html is not mine. I just changed it to suit my needs, so don't think I coded the pages!]
My problem was that I had a lot of fandoms and a lot of tags, so I decided to give my tag page a cover (left pic) and by clicking the fandom one would proceed to the desired category.
Go to "Customize theme" > "Add page" > select "Custom Layout" and paste the code in the crew theme post into the html part.
The cover is a modified version of this crew theme by horan20s. Now the cue is to delete the background image for each member. You are looking for this section:
Delete the url so that the html looks like this:
Now your background will be white and you can rename the different parts as you need them and chose icons instead of the pictures given under CSS.
(If anyone wants it I can make a masterpost with great icon pages I have found during my time on tumblr.)
For every category you need to add a new page to your blog. Every page will contain the code found here made by dominicwrites.
Example: I created the page "http://multifandom-madnesss.tumblr.com/tags", which is my cover. Now I created "/sherlock", "/supernatural" etc. with the tag page code from dominicwrites.
Advice: Modify one page and put in the links without the actual tag:
<div class="btitle">General</div>
<a href="http://multifandom-madnesss.tumblr.com/tagged/">Sherlock crack</a>
<a href="http://multifandom-madnesss.tumblr.com/tagged/">Sherlock meta</a>
And then copy the html into aaaaalll your other pages! AND THEN ADD THE TAGS. I only realized this would make it easier about halfway through the pages, so please learn from my mistakes^^
Anyway, that part takes time because you have to insert the links to the tags so that by clicking on the link you get to see the posts that are tagged accordingly.
Why I chose these themes: The left one allows me to add as many rows as I want, so no matter how many more fandoms I enter, there will always be a space for them on my tag page :) The same with the specific fandom pages - it goes on and on as long as I want to.
I hope that explains it? I had hardly any experience with html before I joined tumblr and all that I know now is the result of hours of hours of trial and error, so don't despair if you try out anything and it doesn't work right away :D
Thanks for reading and thanks to the anon who requested this!