button { color: #23b7cb; font-size: 15px; padding: 5px 15px; background: #fff; border: 1px transparent solid; border-radius: 30px; position: relative; } button:after { content: ''; position: absolute; top: -3px; bottom: -3px; left: -3px; right: -3px; background: linear-gradient(90deg, #000781, #c8cb06); border-radius: 30px; content: ''; z-index: -1; }
<button>进入平台</button>