.converter-box {
        background: #212529; /* Bootstrap dark card color */
        padding: 30px;
        border-radius: 12px;
        box-shadow: 0 4px 15px rgba(0, 0, 0, 0.5);
        width: 100%;
        max-width: 400px;
    } 
    .input-group input,
    .input-group select {
        background-color: #000 !important;  /*Pure black input field*/
         color: #f8f9fa !important;          /*Light text */
        border: 1px solid #444;
    } 
    .input-group input::placeholder {
        color: #aaa;
    } 
    .input-group select {
        border-left: 1px solid #444;
    }
    button {
        border-radius: 50%;
        width: 50px;
        height: 50px;
        display: flex;
        justify-content: center;
        align-items: center;
        margin: 15px auto;
        background-color: #0d6efd; /* Bootstrap primary blue */
        border: none;
    }
     button:hover {
        background-color: #0b5ed7;
    } 
     button i {
        color: #fff;
        font-size: 1.4rem;
    }