Edits to Keyline under header? Squarespace 7.1

Site URL: https://gar-cow-cwsx.squarespace.com/

Hello!

I've added a keyline under my header of 1px. There are two edits I'd like to make.

1. I'd like the keyline to end at the site margins rather than being full bleed (same as the keylines in the footer).

2. I'd like the header keyline ONLY on the projects page to be #38402e  (follow the colour theme - at the moment is isn't visible)

Can anyone help? 

Thanks! 

Site password: bertie 

Q1. First remove this code

.header {
    border-bottom: 1px solid #d2c8cd;
    padding-bottom: 1px;
}

add this code

/* header line */
header#header:after {
    content: "";
    display: block;
    height: 1px;
    width: calc(~"100% - 34px");
    background-color: #d2c8cd;
    margin-left: auto;
    margin-right: auto;
}

Q2. Do Q1 first, then we can check Q2 code.

Thanks @tuanphan That's working for Q1!!

Amazing, sorted. Thanks @tuanphan