Admin: Standardize theme install overlay button height in mobile

[himanshupathak95]

Trac ticket: https://core.trac.wordpress.org/ticket/64999

Fixes .theme-install-overlay .wp-full-overlay-header .button to use the standard mobile button size in mobile views (≤782px), replacing the non-standard 30px/13px values.

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[t-hamano]

Thanks for the PR. Personally, I think it might be better to standardize on the 32px size.

See:

• https://core.trac.wordpress.org/ticket/64689
• #11389

[himanshupathak95]

Thanks for the PR. Personally, I think it might be better to standardize on the 32px size.

Thanks for looking into this. 32px does look more mobile-centric. Incorporated in 954f6c9

[t-hamano]

Thanks for the update! However, I personally suggest the following two changes.

• I propose changing the button height to 32px for non-mobile viewports as well. The 40px button size feels too large for the customizer header.
• Use the new button-compact class: This should eliminate the need to hard-code various styles.