.round {
    position: relative;
}

    .round label {
        background-color: #fff;
        border: 2px solid #66bb6a;
        border-radius: 50%;
        height: 100px;
        position: absolute;
        top: 0;
        width: 100px;
    }

        .round label:after {
            border: 8px solid #66bb6a;
            border-top: none;
            border-right: none;
            content: "";
            height: 20px;
            opacity: 0;
            left: 25px;
            position: absolute;
            transform: rotate(-45deg);
            top: 35px;
            width: 50px;
        }

    .round input[type="checkbox"] {
        visibility: hidden;
    }

        .round input[type="checkbox"]:checked + label {
            background-color: #fff;
            border-color: #66bb6a;
            color: #66bb6a;
        }

            .round input[type="checkbox"]:checked + label:after {
                opacity: 1;
            }