Code only working while in Custo CSS

Site URL: https://www.philcarriere.ca/

Hi,

    I wanted a fixed top header and manage to figure out the coding for it. Everything works perfectly, BUT ... I pushed my luck as I wanted to add some transparency to the header. Everything works fine while editing, but as soon as I am out of the Custom CSS editor and actualizing the page, I lose the transparency.   I am far from being an expert, and I am sure there is a simple solution/explanation to my issue. Thank you for your help.  

.Header.Header--top {
  position: fixed;
  background: #fff9!important;
  top: 0px;
  z-index:1000;
  width:100%;
  box-shadow: 0px 2px 3px rgba(0,0,0,0.1)
}

BTW, the ULR supplied is my current website, the issue is with a new version which is not live yet. 

Thank you!

Try changing hex to rgba color

background: rgba(255, 255, 255,0.6) !important;