.slider-form {
    position: relative;
    display: inline-block;
    width: 70%;
    height: auto;
    background-color: #212121;
    opacity: 0.8;
    padding: 25px;
    margin-left: 100px;
    margin-top: -20px;
}

section.header .maintext {
position: relative;
z-index: 30;
padding-top: 18%;
width: 100%;
display: inline-block;
}

.slider-form .input-group {
    width: 100%;
}

.slider-form .main-heading {
    font-size: 20px;
    text-align: center;
}