doc/themes/learn2-git-sync/scss/theme/_header.scss

#header {
    background: $header-bg;
    color: contrast-color($header-bg, $white);
    text-align: center;

    padding: 1rem;

    a {
        display: inline-block;
    }

    #logo-svg {
        @extend .default-animation;
        width: $logo-width;
        height: $logo-height;

        path {
            @extend .default-animation;
            fill: $white;
        }
    }
}

.searchbox {
    margin-top: 0.5rem;
    position: relative;

    border: 1px solid diminish($header-bg, 5%);
    background: amplify($header-bg, 5%);
    border-radius: 4px;

    label {
        color: rgba($white, 0.8);
        position: absolute;
        left: 10px;
        top: 3px;
    }

    span {
        color: rgba($white, 0.6);
        position: absolute;
        right: 10px;
        top: 3px;
        cursor: pointer;

        &:hover {
            color: rgba($white, 0.9);
        }
    }

    input {
        display: inline-block;
        color: contrast-color(amplify($header-bg, 5%), $white);
        width: 100%;
        height: 30px;
        background: transparent;
        border: 0;
        padding: 0 25px 0 30px;
        margin: 0;
        font-weight: $font-weight-regular;

        @include placeholder {
            color: contrast-color(diminish($header-bg, 5%), $white);
        }
    }
}