Correction:
.alx-tab .tab-item-date { color: #aaa; }
Sometimes the setting is ‘locked’ in parent CSS. Try to override this with !important:
'.alx-tab .tab-item-date { color: #aaa!important; }'
Do you have a child theme?
I have this problem too, on one of my sites. Tried to reinstall, still nothing. Other blog works fine, with plugin search and everything.
