.container {
    width: fit-content;    /* or a fixed width like 600px */
    margin: 40px auto;     /* THIS centers it */
    padding: 20px;
    text-align: center;    /* optional: centers internal text/buttons */
}

.open-btn,
.send-btn {
    padding: 10px 18px;
    border: none;
    background-color: #2b74ff;
    color: white;
    font-size: 1em;
    border-radius: 6px;
    cursor: pointer;
}

.api-box {
    margin-top: 30px;
    padding: 20px;
    border: 1px solid #cccccc;
    border-radius: 8px;
    background: #f9f9f9;
    width: 500px;
}

.api-box input {
    width: 250px;
    padding: 6px;
    margin-left: 8px;
    margin-right: 8px;
}

.api-box select {
    padding: 6px;
    margin-left: 8px;
    margin-right: 8px;
}