blockscout/apps/block_scout_web/assets/css/components/_check.scss

$check-color: $primary !default;
$check-dimensions: 14px !default;

.check {
    align-items: center;
    display: flex;
    position: relative;

    input[type="checkbox"] {
        height: 100%;
        opacity: 0;
        position: absolute;
        width: 100%;
        z-index: 5;

        &:checked + .check-icon::before {
            background-color: $check-color;
            content: "";
            height: 6px;
            left: 50%;
            position: absolute;
            top: 50%;
            transform: translateX(-50%) translateY(-50%);
            width: 6px;
        }
    }

    .check-icon {
        border: 1px solid $base-border-color;
        flex-grow: 0;
        flex-shrink: 0;
        height: $check-dimensions;
        margin: 0 10px 0 0;
        position: relative;
        width: $check-dimensions;
        z-index: 1;
    }

    .check-text {
        font-size: 14px;
        font-weight: normal;
        line-height: 1.2;
        position: relative;
        white-space: nowrap;
        z-index: 1;
    }
}