Once you are comfortable with CSS, try to dig a tad deeper into design philosophies and patterns. Work with established designers who understand that spacing is not just margins/padding of a designated number but a rhythm across screens of varying shapes and sizes.
For instance, understand the reasoning why a good designer will tell you that the typographic scale for desktops will be major-third, while for the smaller mobile phones, it will have to be minor-third.
Advance topics to research and have peace with CSS are vertical rhythm for spacings, modular scaling for typography, and the Cicada Principle, etc.
Here is an anecdote to illustrate the above;
There was a "Careers Page" redesign for one of the biggest banks in the world - after about 10+ years of their old one. When I landed in London, they already had a "Senior front-end developer" mid-way into the project. I went as a replacement for one of my team who had a family emergency. I haven't written much code in years.
They had engaged a brilliant designer and had a wall plastered with some of the most beautiful glossy print-outs. Everyone, including the client, loved it. Unfortunately, the struggle was -- the front-end output had irregular margins (pixel mismatch), fix another but breaks the other, etc.
I saw that they had screen rulers that try to match the design with what comes out on the screen.
I requested the designer to spend few hours explaining his reasoning behind the spacing and asked him the rhythms (similar to musical notes) that he has used, the scaling of the font sizes. This was when I realized the designer was brilliant, but the engineers would not understand or appreciate his effort.
I wrote out the Sass functions and mixins and steadily replaced many hacked in numbers and values. Introduced Design Tokens, a simple style guide, etc.
The website is still there and will likely last another 10+ years. I'm also sure many of you might have stumbled on it or have applied to jobs with it. :-)