My customization to GitHub Ice Dark theme for Stylish chrome extension.

custom.css

button[type="button"].repository-lang-stats-graph {
    background: transparent !important;
    opacity: 0.5 !important;
}

.hook-delivery-container pre {
    background-color: inherit;
}

div.gh-header, .gh-header .gh-header-sticky.is-stuck+.gh-header-shadow, .pagination-loader-container {
    background: #212121 !important;
}

.select-menu-item.navigation-focus, .select-menu-item.navigation-focus .description-inline, .select-menu-item.navigation-focus.select-menu-action, .select-menu-item.navigation-focus.selected, .select-menu-item:focus, .select-menu-item:focus .description-inline, .select-menu-item:focus.select-menu-action, .select-menu-item:focus.selected, .select-menu-item:hover, .select-menu-item:hover .description-inline, .select-menu-item:hover.select-menu-action, .select-menu-item:hover.selected, .select-menu-item[aria-checked=true]:focus, .select-menu-item[aria-checked=true]:hover, .select-menu-item[aria-selected=true] .description-inline, .select-menu-item[aria-selected=true].select-menu-action, .select-menu-item[aria-selected=true]:focus, .select-menu-item[aria-selected=true]:hover {
    background: rgb(160, 180, 200) !important;
    color: #111 !important;
}

/* color of the code highlighting */
.blob-code-inner.highlighted, .blob-code-inner .highlighted {
    background-color: rgba( 255, 251, 221, 0.1 );
    border-left: 2px solid #bf7e08 !important;
}

.TimelineItem-badge.bg-green, .bg-green {
    background-color: #17b53b !important;
}

.TimelineItem-badge.bg-red, .bg-red {
    background-color: #911 !important;
}

.blob-code.highlighted { padding-left: 8px }

/* comments should not be larger than a regular code font */
.pl-c, .pl-c span {
    font-size: inherit !important;
}

.bg-blue-light {
    background-color: inherit !important;
}

.related-issue-item.navigation-focus, .similar-issue-item.navigation-focus {
    background-color: rgb(100, 89, 12) !important;
}

.bg-blue-2, .bg-blue, .discussion-item-changes-marker.is-unread .discussion-item-icon {
    background-color: #045a8c !important;
}

.Progress {
    background-color: #343434;
}

.timeline-comment, .review-comment {
    color: #fafbfc !important;
}

.TimelineItem-badge, .TimelineItem:before {
    background-color: #343434 !important;
    color: #fafbfc;
}

.TimelineItem-break {
    background-color: #212121 !important;
    border-top: 4px solid #343434 !important;
}

.Box-row--focus-gray.navigation-focus > .d-table {
    /* box-shadow: 2px 0px 0px 0px #bf7e08 inset !important; */
    background: linear-gradient( 90deg, transparent 0%, transparent 0.49%, #bf7e08 0.5%, transparent 0.8% );
}