How to change the color of the line below the top navigation

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4

I think it’s this box-shadow

.d-header {
    width: 100%;
    position: absolute;
    top: 0;
    z-index: 1001;
    background-color: #fff;
    box-shadow: 0 2px 4px -1px rgba(0,0,0,0.25);
}