Navigation bar with gradient colour palette

Site URL: https://www.pppartners.sg/

Hi,

Does anyone know how I can set my navigation bar with colour gradient? 

I set a picture in my home page top section (first picture) and I like this colour gradient so I was thinking if it is possible to have this colour gradient as my navigation background when I go to the other pages to make it more "standardise" but I am not sure how to work around with it. 

If setting a colour gradient as my navigation background is impossible, how can I set colour to my navigation background? I tried playing around with it (second picture) but doesn't seem possible.  

Hi. What is access password?