PTB-fe/styles/app/layout/settings.scss

// Used for theme swticher
.setting-color {
    padding: 0 5px;

    >label {
        display: block;
        position: relative;
        margin: 0 10px;
        border-radius: 3px;
        overflow: hidden;
        border: 1px solid rgba(0, 0, 0, .1);
        cursor: pointer;

        &:first-child {
            margin-left: 0
        }
        &:last-child {
            margin-right: 0
        }

        $baseHg: 15px;
        >.color {
            display: block;
            height: $baseHg * 1.2;
        }

        >.split {
            @include clearfix();
            display: block;
            >.color {
                display: block;
                height: $baseHg * 2.5;
                &:first-child {
                    float: left;
                    width: 70%;
                }
                &:last-child {
                    float: right;
                    width: 30%;
                }
            }
        } // icon checked
        >.icon-check {
            position: absolute;
            display: block;
            left: 50%;
            top: 50%;
            width: 20px;
            height: 20px;
            margin-top: -20px;
            margin-left: -10px;
            text-align: center;
            font-size: 1.33333333em;
            vertical-align: -15%;
            color: #fff;
            opacity: 0;
        }

        >input[type="radio"] {
            position: absolute;
            opacity: 0;
            visibility: hidden;
            &:checked+.icon-check {
                opacity: 1 !important;
            }
        }
    }
}