You don’t have to. That’s what your teammates are for.
I’ve been a programmer and web server admin for over 20 years and here to get up to speed with front-end development (notice I didn’t say frameworks). My forte certainly isn’t design, but I still enjoy doing it and if I do it myself, it means I don’t have to rely on someone else to do it for me.
Why do you feel that it’s holding you back? Plenty of free templates (some that include the html/css) out there that you can use if you want to do web development, but don’t want to do the design (or front-end) part. So long as you have some knowledge with HTML/CSS you can customize any template to suit your needs.
If you have found something that you are passionate about, focus on that, it will keep you motivated and wanting to learn more. Curiosity is an great skill to have in this industry. Tune out the people who tell you that you shouldn’t be learning “xyz technology”, that IMO, is asinine advice. There is never any waste in picking up a new skill in this industry, besides which, it makes you more employable, and granted that you get the fundamentals of programming, it will make you a better programmer. Especially if you can explain and weigh the pros and cons of using different tech stacks in different scenarios. This will come with hands on experience and working on a variety of projects.
Do you know the type of work you’d like to do or types of organizations you’d like to work for? If you know those things, you can search out their jobs postings and see what skill set is required.