fix: background color of search box shortcut key

[mukul98s]

Well detailed description of the change :

 I worked on the search box shortcut key's styling. 

Context of the change :

 - Why is this change required ?
 - The current background of the "/" does not looks great. It feels like an broken piece. 

• Does it solve a problem ? (please link the issue)

Type of change :

• New feature

Preview (Screenshots) :

I do not change the actual size of the search box.

Before

After

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the STYLE_GUIDE of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• All new and existing tests passed.

Reviewers

@codyseibert , @divanov11

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