WordPress – Portfolio – Change variety of objects in a row

I’m utilizing the Pure theme. As a substitute of getting 5 (5) objects per row within the portfolio, I wish to have 4 (4).

How may I customise the theme’s CSS? To construct the web page, I’m utilizing the portfolio module of the GT3 Web page Builder.The CSS is beneath:

/* Portfolio */

.optionset {
    margin: 0;
    padding-left: 0;
    text-align: heart;
    line-height: 13px;
}

.optionset li {
    list-style: none;
    margin-left: 0 !necessary;
    margin-right: 30px;
    show: inline-block;
    line-height: 13px;
}

.optionset li:last-child {
    margin-right: 0;
}

.optionset li:earlier than {
    show: none !necessary;
}

.optionset li a {
    shade: #484848;
    font-size: 13px;
    line-height: 13px;
}

.optionset li a:hover, .optionset li.chosen a {
    shade: #bfbfbf;
}

.portfolio_item {
    width: 20%;
    margin-bottom: 40px;
}

.portfolio_item .innerpadding {
    padding-left: 50px;
}

.portwrap {
    margin-left: -50px;
}

.portfolio_block {
    margin-top: 68px;
}

.isotope_preloader {
    /*opacity: 0;*/
    min-height: 700px;
}