Darkmode fix#298

[Kartikay304]

Fixes #298

Changes done:

• [x] Changed the label from "Edit on Github" to "Toggle Dark Mode"
• [x] Removed on click property ,which was responsible for label to redirect to Github.

Screenshots:

Before -

After -

Preview Link(s):

✅️ By submitting this PR, I have verified the following

• [x] Checked to see if a similar PR has already been opened 🤔️
• [x] Reviewed the contributing guidelines 🔍️
• [x] Sample preview link added (add a link from the checks tab after checks complete)
• [x] Tried Squashing the commits into one @ShreyaPrasad1209, Will you please take a look at my PR :-).

[ShreyaPrasad1209]

@tachyons is it wise to edit the docs theme?

[tachyons]

No, we may have to fix in upstream

[Kartikay304]

No, we may have to fix in upstream

Then will you tell me which file I need to edit, as I am not able to find any other .css file in current repo