.header {
    display: flex;
    align-items: center;
    justify-content: flex-start;
    height: 50px;
    width: 100%;
    /* Frutiger Aero gradient */
    background: 
        linear-gradient(to right, #02000fff 0%, #02000f00 3px, #a3fcff00 calc(100% - 3px), #a3fcffff 100%),
        linear-gradient(to bottom, #a3fcff 0%, #00a6ff 10%, #1900ff 90%, #02000f 100%);
    background-blend-mode: normal;
}

.header_cell {
    width: 120px;
    max-width: 120px;
    height: 80%;
    /* Center the text inside*/
    text-align: center;
    vertical-align: middle;


    position: relative;
    color: #ffffff;
    font-weight: bold;
    cursor: pointer;
    transition: background-color 0.3s ease;
    background: 
        linear-gradient(to right, #02000fff 0%, #02000f00 3px, #a3fcff00 calc(100% - 3px), #a3fcffff 100%);

}
/*check if screen is horizontally smaller than 640px*/
@media screen and (max-width: 640px) {
    .header_cell {
        width: 70px;
        max-width: 70px;
        min-width: 70px;
        /*padding: 10px 20px;*/
    }
}
.header_cell a, .header_cell a:visited, .header_cell a:link{
    color: #ffffff;
    text-decoration: none;
}
@media (pointer: course), (pointer: fine) {
    .header_cell a, .header_cell a:visited, .header_cell a:link{
        width: 100%;
        height: 100%;
        display: inline-block;
    }
}

.header_cell:hover {
    background-color: rgba(255, 255, 255, 0.1); /* Adds a hover effect */
}

/* Dropdown menu */
.dropdown {
    position: relative;
}

.dropdown-content {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    background-color: #ffffff;
    min-width: 160px;
    box-shadow: 0px 8px 16px rgba(0, 0, 0, 0.2);
    z-index: 1;
}

.dropdown-content a {
    color: #000000 !important;
    padding-top: 10px;
    padding-bottom: 10px;
    padding-left: 10px;
    padding-right: 0px;
    max-width: calc(100% - 10px);

    text-decoration: none;
    display: block;
    text-align: left;

    background: linear-gradient(to bottom, #ffffff 0px, #eaeaea 4px, #d5d5d5 calc(100% - 3px), #cccccc 100%) !important;
}

.dropdown-content a:hover {
    background-color: #ddd !important;
}

.header_cell:hover .dropdown-content {
    display: block;
}