@mixin hide-line-numbers {
    float: left;
    margin-left: -20px;

    width: 20px;
    height: 100%;
    padding: 0;
    overflow: hidden;

    color: white;
    text-align: right;

    &:hover, &:active {
        color: #ccc;
        background-color: #CCC;
    }

    &:before {
        content: "#";
        display: block;
        float: left;
        width: 9px;
        height: 100%;
        overflow: hidden;
        border-right: 1px solid #ccc;
    }

    @include min-screen(240px) {
        width: 30px;
        margin-left: -30px;

        &:before {
            width: 14px;
        }
    }
}


.anchor {
    @include hide-line-numbers;

    @include min-screen(320px) {
        /* Show line numbers. */
        margin-left: -50px;
        width: 44px;
        height: auto;
        padding: 2px;
        text-align: center;
        color: #ccc;

        &:before {
            display: none;
        }
    }
}

@include min-screen(320px) {
    .always-hide-line-numbers {
        /* Cancel showing line numbers. */
        .anchor {
            @include hide-line-numbers;
        }
    }
}