JSFiddle - React, Tailwind, and code Playground

HTML

<input type="submit" class="btn_enter_reg" disabled="disabled">

CSS

.btn_enter_reg {
    margin-top: 10px;
    cursor: pointer;
    border: none;
    font-size: 14px;
    color: #fff;
    border-radius: 5px;
    padding: 15px 50px 15px 50px;
    box-shadow: 0 2px 2px #005d71;
    text-decoration: none;
    background: #00a6ca;
    background: -moz-linear-gradient(90deg, #0094bc 0, #00a6ca 100%);
    background: -webkit-gradient(linear, 90deg, color-stop(0%, #0094bc), color-stop(100%, #00a6ca));
    background: -webkit-linear-gradient(90deg, #0094bc 0, #00a6ca 100%);
    background: -o-linear-gradient(90deg, #0094bc 0, #00a6ca 100%);
    background: -ms-linear-gradient(90deg, #0094bc 0, #00a6ca 100%);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#0094bc', endColorstr='#00a6ca', GradientType='0');
    background: linear-gradient(0deg, #0094bc 0, #00a6ca 100%)
}

btn_enter_reg[disabled] {
    background: #dadada;
    color: #B8B8B8;
    box-shadow: 0 2px 2px #565656
}