One suggestion - if you get 10 plain black t-shirts, then implement your style!

I am a dev who was focused on design and ux early on (this has changed as the needs of my work changed).

@abhideckert's suggestion on how to analyze the needs is great. Now on to the implementation.

Similarly to development, you start out with some requirements - you need to show an input box, a history of inputs, and a sidebar with categories. You work out the layout (with wireframes, pencil drawings, etc.). Then comes visual style, which I guess is the thing you struggle with?

In both layout and visual style, you need to apply design principles, but ultimately the goal is to guide the visitor's eye to the right places. This is where rhythm, repetition and contrast play a role. Basically highlight important elements, make the order of elements logical and not boring, avoid large empty areas but leave sufficient "breathing room" between elements, etc.

For visual style, you should make your own "style guide" that you apply to all personal projects. You can vary it a bit for each, if you are worried about them looking the same. Make that into a css file with a dummy html page to test. Add an input box, a textarea, select, unordered lists, etc. and style all of them to your liking. This guide will capture a lot of visual ideas, colors, spacing, which you can paste straight into your project. Do not sweat too much about stealing other people's ideas - it's an intrinsic property of art, and anyway it will probably not look 100% the same even if you copy it.

Edit: PS: spend some time just looking at the design and thinking.