So my advise is first concentrate on your studies. Make sure you are graduating with at least first class.
Blogging can be great career but not for all. I m not saying stop blooging, but let it be part time. Believe me college days are best days in life make sure to enjoy that phase. I know blooging takes lot of personal time sitting in front of computers and screwing up personal Time
Regarding your question,
Theme are generally designed using html, CSS and php. You should also know MySQL or mariadb databases.
As someone said, do whatever you do best. If you are good at content, outsource theme and design. It doesn’t make sense to learn theme design.
It is my personal experience I wanted to design website. I learned html, CSS and bootstrap and little bit jQuery. Believe me I can not design theme. I don’t have that skill. I am good at coding but not at design. Then I came across WordPress. It is too easy and now I have own site. Now I realized, there was no need to learn coding, rather I should have spent that time on content.
Choice is yours are you good in coding or writing…?