SOURCE

<div class="title">径向渐变应用（tabs）：</div>
<div class="browser">
    <div class="header">
        <div class="circle-tab">
            <svg class="close-icon" xmlns="http://www.w3.org/2000/svg" width="1em" height="1em" viewBox="0 0 24 24"><path fill="currentColor" d="m13.41 12l4.3-4.29a1 1 0 1 0-1.42-1.42L12 10.59l-4.29-4.3a1 1 0 0 0-1.42 1.42l4.3 4.29l-4.3 4.29a1 1 0 0 0 0 1.42a1 1 0 0 0 1.42 0l4.29-4.3l4.29 4.3a1 1 0 0 0 1.42 0a1 1 0 0 0 0-1.42Z"/></svg>
        </div>
    </div>
</div>

<div class="title">径向渐变：</div>
<div class="gradient-wrap">
	<div class="gradient-box"></div>
	<div class="gradient-box"></div>
	<div class="gradient-box"></div>
    <div class="gradient-box"></div>
</div>

.title {
    margin-bottom: 10px;
}
/* radial-gradient */
.gradient-wrap {
    display: flex;
    margin-bottom: 20px;
}

.gradient-box {
    flex: 1;
    height: 150px;
    border: 1px solid #000;
}

.gradient-box +.gradient-box {
    margin-left: 20px;
}

.gradient-box:nth-of-type(1) {
    background: radial-gradient(#e66465, #9198e5);
}

.gradient-box:nth-of-type(2) {
    background: radial-gradient(closest-side, #3f87a6, #ebf8e1, #f69d3c);
}

.gradient-box:nth-of-type(3) {
    background: radial-gradient(circle at 100%, #333, #333 50%, #eee 75%, #333 75%);
}

.gradient-box:nth-of-type(4) {
    background: radial-gradient(ellipse at top, #e66465, transparent), radial-gradient(ellipse at bottom, #4d9f0c, transparent);
}

.browser {
    height: 200px;
    border: 1px solid #b6b6b6;
    border-radius: 10px;
}

.header {
    height: 40px;
    background: #d3e3fd;
    border-radius: 10px 10px 0 0;
}


/* .circle-tab */

.circle-tab {
    position: relative;
    top: 4px;
    left: 40px;
    background: #fff;
    border-radius: 10px 10px 0 0;
    width: 130px;
    height: 36px;
}

.circle-tab::before {
    content: '';
    position: absolute;
    width: 13px;
    height: 13px;
    left: -13px;
    bottom: 0;
    background: #000;
    /*圆形 渐变的圆心在左上 透明 20px大小 渐变到 #d3e3fd 21px大小*/
    background: radial-gradient(circle at 0 0, transparent 13px, #fff 13px);
}

.circle-tab::after {
    content: '';
    position: absolute;
    width: 13px;
    height: 13px;
    right: -13px;
    bottom: 0;
    background: #000;
    /* 渐变的圆心在右上 */
    background: radial-gradient(circle at 100% 0, transparent 13px, #fff 13px)
}

.close-icon {
    position: absolute;
    right: 10px;
    top: 50%;
    color: #1f1f1f;
    transform: translateY(-50%);
}

.close-icon:hover {
    background: #dcdcdd;
    border-radius: 50%;
}