CSS3边框圆角知识

    <div class="item" data-brief="整圆">
    <div class="border-radius"></div>
    </div>
/*整圆*/
        .item:nth-child(1) .border-radius {
            border-radius: 90px;
        }

    <div class="item" data-brief="拱形">
    <div class="border-radius"></div>
    </div>
/*拱形*/
        .item:nth-child(2) .border-radius {
            border-radius: 90px 90px 0 0;
        }

            <div class="item" data-brief="半圆">
                <div class="border-radius"></div>
            </div>
/*半圆*/
        .item:nth-child(3) .border-radius {
            height: 90px;
            border-radius: 90px 90px 0 0;
        }

            <div class="item" data-brief="左上角">
                <div class="border-radius"></div>
            </div>
/*左上角*/
        .item:nth-child(4) .border-radius {
            /*height: 90px;*/
            border-radius: 90px 0 0 0;
        }

            <div class="item" data-brief="四分之一圆">
                <div class="border-radius"></div>
        </div>
/*四分之一圆*/
        .item:nth-child(5) .border-radius {
            width: 90px;
            height: 90px;
            border-radius: 90px 0 0 0;
        }

            <div class="item" data-brief="横着的椭圆">
                <div class="border-radius"></div>
            </div>
/*横着的椭圆*/
        .item:nth-child(6) .border-radius {
            height: 90px;
            /*border-radius: 50%;*/
            border-radius: 90px 90px 90px 90px / 45px 45px 45px 45px;
            /*border-radius: 45px / 90px;*/
        }

            <div class="item" data-brief="竖着的椭圆">
                <div class="border-radius"></div>
            </div>
    /*竖着的椭圆*/
        .item:nth-child(7) .border-radius {
            width: 90px;
            border-radius: 45px 45px 45px 45px / 90px 90px 90px 90px;
        }

            <div class="item" data-brief="半个横着的椭圆">
                <div class="border-radius"></div>
            </div>
    /*半个横着的椭圆*/
        .item:nth-child(8) .border-radius {
            height: 45px;
            border-radius: 90px 90px 0 0 / 45px 45px 0 0;
        }

            <div class="item" data-brief="半个竖着的椭圆">
                <div class="border-radius"></div>
            </div>
    /*半个竖着的椭圆*/
        .item:nth-child(9) .border-radius {
            width: 45px;
            border-radius: 45px  0 0 45px / 90px 0 0 90px;
        }

            <div class="item" data-brief="四分之一竖着的椭圆">
                <div class="border-radius"></div>
            </div>
        /*四分之一竖着的椭圆*/
        .item:nth-child(10) .border-radius {
            width: 45px;
            height: 90px;
            border-radius: 45px 0 0 0 / 90px 0 0 0;
        }

            <div class="item" data-brief="饼环">
                <div class="border-radius"></div>
            </div>
    /*饼环*/
        .item:nth-child(11) .border-radius {
            width: 40px;
            height: 40px;
            border: 70px solid red;
            border-radius: 90px;
        }

            <div class="item" data-brief="圆饼">
                <div class="border-radius"></div>
            </div>
    /*圆饼*/
        .item:nth-child(12) .border-radius {
            width: 40px;
            height: 40px;
            border: 70px solid red;
            border-radius: 60px;
        }

            <div class="item" data-brief="左上角圆饼">
                <div class="border-radius"></div>
            </div>

.item:nth-child(13) .border-radius {
            width: 60px;
            height: 60px;
            border: 60px solid red;
            border-radius: 90px 0 0 0;
        }

            <div class="item" data-brief="对角圆饼">
                <div class="border-radius"></div>
            </div>

/*对角圆饼*/
        .item:nth-child(14) .border-radius {
            width: 60px;
            height: 60px;
            border: 60px solid red;
            border-radius: 90px 0 90px 0;
        }

            <div class="item" data-brief="四边不同色">
                <div class="border-radius"></div>
            </div>

        /*四边不同色*/
        .item:nth-child(15) .border-radius {
            width: 0px;
            height: 0px;
            border-width: 90px;
            border-style: solid;
            border-color: red green yellow blue;
        }

            <div class="item" data-brief="右透明色">
                <div class="border-radius"></div>
            </div>
        <div class="item" data-brief="圆右透明色">
                <div class="border-radius"></div>
            </div>
/*右透明色*/
        .item:nth-child(16) .border-radius {
            width: 0px;
            height: 0px;
            border-width: 90px;
            border-style: solid;
            border-color: red green yellow blue;
            border-right-color: transparent;
        }

            <div class="item" data-brief="圆右红透明色">
                <div class="border-radius"></div>
            <    /*圆右透明色*/
        /*圆右红透明色*/
        .item:nth-child(18) .border-radius {
            width: 0px;
            height: 0px;
            border-width: 90px;
            border-style: solid;
            border-color: transparent;
            border-right-color: red;
            border-radius: 90px;
        }/div>

            <div class="item" data-brief="阴阳图前世">
                <div class="border-radius"></div>
            </div>

        /*阴阳图前世*/
        .item:nth-child(19) .border-radius {
            width: 180px;
            height: 0px;
            border-top-width: 90px;
            border-bottom-width: 90px;
            border-style: solid;
            border-top-color: red;
            border-bottom-color: green;
            /*border-right-color: red;*/
            border-radius: 90px;
        }

            <div class="item" data-brief="阴阳图前世2">
                <div class="border-radius"></div>
            </div>
    /*阴阳图前世2*/
        .item:nth-child(20) .border-radius {
            width: 180px;
            height: 90px;
            border-bottom-width: 90px;
            border-style: solid;
            border-bottom-color: green;
            background-color: red;
            /*border-right-color: red;*/
            border-radius: 90px;
        }
            <div class="item" data-brief="阴阳图今生">
                <div class="border-radius"></div>
            </div>
    /*阴阳图今生*/
        .item:nth-child(21) .border-radius {
            width: 180px;
            height: 90px;
            border-bottom-width: 90px;
            border-style: solid;
            border-bottom-color: green;
            background-color: red;
            border-radius: 90px;
            position: relative;
        }

        .item:nth-child(21) .border-radius::after,
        .item:nth-child(21) .border-radius::before {
            content: '';
            position: absolute;
            top: 50%;
            width: 20px;
            height: 20px;
            /*margin: -10px 0 0 0;*/
            border-width: 35px;
            border-style: solid;
            border-radius: 45px;
        }

        /*左阴阳*/
        .item:nth-child(21) .border-radius::after {
            background-color: red;
            border-color: green;
        }

        /*右阴阳*/
        .item:nth-child(21) .border-radius::before {
            background-color: green;
            border-color: red;
            right: 0;
        }

        /*右阴阳*/
        .item:nth-child(22) .border-radius {
            width: 180px;
            height: 90px;
            border-bottom-width: 90px;
            border-bottom-color: green;
            border-bottom-style: solid;
            background-color: red;
            border-radius: 90px;
            position: relative;
        }

            <div class="item" data-brief="阴阳图今生2">
                <div class="border-radius"></div>
            </div>
.item:nth-child(22) .border-radius::after,
        .item:nth-child(22) .border-radius::before {
            content: '';
            position: absolute;
            top: 50%;
            width: 20px;
            height: 20px;
            border-width: 35px;
            border-style: solid;
            border-radius: 45px;
        }

        .item:nth-child(22) .border-radius::before {
            border-color: green;
            background-color: red;
        }

        .item:nth-child(22) .border-radius::after {
            right: 0;
            border-color: red;
            background-color: green;
        }
            <div class="item" data-brief="消息框">
                <div class="border-radius"></div>
            </div>
    /*消息框*/
        .item:nth-child(23) .border-radius {
            width: 160px;
            height: 80px;
            background-color: red;
            border-radius: 6px;
            position: relative;
        }

        .item:nth-child(23) .border-radius::after {
            content: '';
            width: 0;
            height: 0;
            border-width: 10px;
            border-style: solid;
            border-color: transparent;
            border-right-color: red;
            position: absolute;
            top: 16px;
            left: -20px;
        }

            <div class="item" data-brief="奇怪的图形">
                <div class="border-radius"></div>
            </div>
    /*奇怪的图形*/
        .item:nth-child(24) .border-radius {
            width: 40px;
            height: 40px;
            border-width: 45px 0 45px 70px;
            border-style: solid;
            border-radius: 0 0 60px 0;
            border-color: red;
        }
            <div class="item" data-brief="奇怪的图形2">
                <div class="border-radius"></div>
            </div>
    .item:nth-child(25) .border-radius {
            width: 100px;
            height: 40px;
            border-width: 45px 20px 45px 70px;
            border-style: solid;
            border-radius: 60px;
            border-color: red;
        }
            <div class="item" data-brief="QQ对话">
                <div class="border-radius"></div>
            </div>
/*QQ对话*/
        .item:nth-child(26) .border-radius {
            width: 160px;
            height: 80px;
            background-color: red;
            border-radius: 6px;
            position: relative;
        }

        .item:nth-child(26) .border-radius::after {
            content: '';
            position: absolute;
            top: 0;
            right: -20px;
            width: 30px;
            height: 30px;
            border-width: 0 0 30px 30px;
            border-style: solid;
            border-bottom-color: red;
            border-left-color: transparent;
            border-radius: 0 0 60px 0;
        }

            <div class="item" data-brief="圆角百分比">
                <div class="border-radius"></div>
            </div>
               /*圆角的百分比设置 */
        .item:nth-child(27) .border-radius {
            width: 180px;
            /*height: 180px;*/
            height: 90px;
            border-radius: 50%;
            border-radius: 90px/45px;

            /*百分比是按横竖两个对应的方向的长度进行计算*/
        }