Hello,
Please try the next code:
.content-page .null-instagram-feed:not(.sidebar-widget):not(.footer-widget) .widget-title {
font-size: calc(var(--h5-size-proportion) * 1rem);
color: var(--et_dark-2-white);
margin-bottom: 1.4em !important;
padding-bottom: 1em;
border-bottom: 1px solid var(--et_border-color);
text-align: left;
}
Regards