Input/Output indicators

[LoganJFisher]

Is your feature request related to a problem? Please describe.
Right now, if I input 2+2, the next cell will show 4, but there is no indication at a glance of what is an input and what is an output.

Describe the solution you'd like
Mathematica resolves this by indicating to the left of each cell: "In[#]=" or "Out[#]=", which I believe is the most elegant way of resolving this issue.

Additional context
WLJS:
Mathematica:

[munuxi]

Yes, we need it, and it's very useful when we want to use output result as our variables e.g. %234 in the calculation.

[JerryI]

In principle, this is indicated by a gray bracket. But anyway, i will try to find a place in HTML layout for additional labels

[JerryI]

We need UI designer ;D