.menu-flex li {background:rgba(0,0,0,.5); border:2px #fff solid;}
input[type=text], textarea {background:rgba(0,0,0,.3); border:2px #000 solid; }
input[type=submit] {border:2px #000 solid; background:rgba(0,0,0,.6); } 
.next-section, .menu-flex li {
    background: rgba(0,0,0,.5);
    border: 2px #fff solid;
}
.next-section:hover {color:yellow;}
input[type=submit]:hover {color:yellow;}
* {transition:.4s;}