Changing the Customer Portal header color

Changing the Customer Portal header color

Dear Zoho team,

I'm trying to change the customer portal color because my logo is in white and when i click on Sign in, the portal has a gray background and I can barely see my logo. 

I'm trying the following custom CSS which works in the inspector but not in the actual site: 

.portal-site-detail-container {
    background-color: #081C20;
}

Please help me out! 

Best regards.

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