:root {
    --theme-background-color: white;
    --theme-button-background-color: #d9001d;
    --theme-font-color: #ffffff;
    --theme-body-title-font: plex-sans,sans-serif;
    --theme-body-font: "plex-sans","Helvetica Neue",Helvetica,Arial,"Microsoft YaHei","?????","Hiragino Sans GB","????",sans-serif;
    --theme-body-color: #2e3333;
    --theme-input-title-color: #000000;
    --theme-form-container-color: #495057;
    --theme-form-container-background-color: #fff;
    --theme-form-container-border-color: #ced4da;
}
#btn-submit {
    background-color: var(--theme-button-background-color);
    color: var(--theme-font-color);
}
.div_nif {
    display: flex;
    gap: 10px; /* Espacio entre los inputs */
    margin-top: 5px;
}
#iso_nif {
    flex: 0 0 40px; /* ancho fijo de 80px */
}
#nif {
    flex: 1;        /* ocupa el resto del espacio disponible */
    min-width: 0;
}