How to decrease Hestia Post header height

If you'd like to decrease the area below and above the header then please go to Appearance->Customize->Additional CSS and add the following:

.page-header.header-small .container{
padding-top:  86px !important;
padding-bottom: 67px !important; 

Adjust the top and bottom padding as you wish by changing the number value. The least the bottom padding can go down to is 67px.

Save your changes and that's it!