src/style.css

/* Increase the font size and make the expander label bold */
div[data-testid="stExpander"] div[role="button"] p {
    font-size: 1.5rem !important;   /* Increase font size */
    font-weight: bold !important;   /* Make bold */
}

/* Change background color on hover */
[data-testid="stExpander"] details:hover summary {
    background-color: rgba(198, 151, 183, 0.68);
    border-radius: 6px;
    transition: 0.3s ease;
}

/* Change background and text color when expanded */
[data-testid="stExpander"] details[open] summary {
    background-color: rgba(10, 28, 226, 0.765);
    color: #fff; /* White text */
    border-radius: 6px;
}