Bootstrap4导航栏切换器未显示

这是我第一次使用Bootstrap 4 beta.我有一个慈善团体网站,我现在在BS3中制作并运行.我正在使用固定的顶部导航栏和自定义CSS.当网站查看较小而不是全屏时,切换图标不会显示.你能帮助我吗？我希望它像导航链接一样是白色的,并且悬停会更改要读取的链接.这是头部链接

    

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js代码链接在页面底部

这是我的代码.

/* Navbar */

.navbar-custom {
    background-color: #3193de;
}


/* change the brand and text color */

.navbar-custom .navbar-brand,
.navbar-custom .navbar-text {
    text-decoration: none; color: #fff;
}


/* change the link color */

.navbar-custom .navbar-nav .nav-link {
   text-decoration: none; color: #fff;
}


/* change the color of active or hovered links */

.navbar-custom .nav-item.active .nav-link,
.navbar-custom  {
  text-decoration: none;  color: #fff;
}

.nav-item .nav-link:hover {
    text-decoration: none; color: #ff0000;
}

/* for dropdown only - change the color of dropdown */

.navbar-custom .dropdown-menu {
    background-color: #3193de;
}

.navbar-custom .dropdown-item {
    text-decoration: none; color: #fff;
}

.navbar-custom .dropdown-item:hover,
.navbar-custom .dropdown-item:focus {
    text-decoration: none; color: #ff0000;
    background-color:#3193de;
}
.navbar-header .navbar-toggler {
  border: 0;
}
.navbar-toggler-icon {
  color: #fff;
}
.navbar-toggler-icon:hover {
  background: #ff0000;
}

.navbar-toggler-icon {
        background-image: url("data:image/svg+xml;charset=utf8,%3Csvg viewBox='0 0 32 32' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath stroke='rgba(255,255,255, 1)' stroke- stroke-linecap='round' stroke-miterlimit='10' d='M4 8h24M4 16h24M4 24h24'/%3E%3C/svg%3E");
}

stroke='rgba(255,255,255, 1)'