When clicking on Search button, Search bar overlaps with buttons (Search, Directory, View mode, Sort, Create a New Channel)
Search bar opening under the buttons, or hiding buttons
Search bar overlaps with buttons, displaying both things together

I cannot reproduce this error in v0.63.3. Tested with Windows (Desktop Client, Chrome 65.0.3325.181) and Mac (Desktop Client, Chrome 65.0.3325.181).
Can you please provide more informations about your system?
@kaiiiiiiiii Thanks for the quick reply!
I updated the case with some data I could collect. Hope it helps.
We solved it! There was a wrong value at "Primary Darkest" color. Thanks!
I still see the error on 0.65.1

Is there a fix via configuration?
@qasim-arbisoft Have you tried changing Primary Darkest?
Administration → Layout → Primary Darkest
Check its setting, if it is invalid the background of the Search field will be transparent. This is working as intended~
Thanks @vynmera . It's fixed now!