All code are beautifully written. You can customize easily. Just look the amex/icon.html file go to form code with change and use.you would like to edit a specific section of the site, simply find the appropriate label in the and change what you need.
amex bootstrap 4 admin dashboard provide this beautifull with standard button form you can see this documentation
Font awesome
fa-500px
lni-add-file
lni-agenda
lni-alarm
lni-alarm-clock
lni-amazon
fa-address-card
lni-ambulance
lni-amex
lni-anchor
lni-android
lni-android-original
lni-angle-double-down
lni-angle-double-left
lni-angle-double-right
lni-angle-double-up
lni-apartment
lni-apple
lni-archive
lni-arrow-down
lni-arrow-down-circle
lni-arrow-lef
lni-arrow-left-circle
lni-arrow-right
lni-arrow-right-circle
lni-arrow-top-left
lni-arrow-top-right
lni-arrow-up
lni-arrow-up-circle
lni-arrows-horizontal
lni-arrows-vertical
lni-backward
lni-baloon
lni-ban
lni-bar-chart
lni-basketball
lni-behance
fa-angry
lni-behance-original
lni-bitbucket
lni-bitcoin
lni-blackboard
lni-blogger
lni-bluetooth
lni-bold
lni-bolt
lni-bolt-alt
lni-book
lni-bookmark
lni-bookmark-alt
lni-bootstrap
lni-brick
lni-bridge
lni-briefcase
lni-brush
lni-brush-alt
lni-bubble
lni-bug
lni-bulb
fa-arrow-circle-left
fa-arrow-circle-right
fa-arrow-circle-up
lni-bullhorn
lni-calculator
lni-calendar
lni-camera
lni-candy
lni-candy-cane
lni-capsule
lni-car
lni-car-alt
fa-asterisk
lni-caravan
fa-at
lni-check-box
lni-check-mark-circle
fa-audible
fa-audio-description
lni-chevron-down-circle
lni-chevron-left
lni-chevron-left-circle
lni-chevron-right
lni-chevron-right-circle
lni-chevron-up
lni-chevron-up-circle
lni-chrome
lni-circle-minus
lni-close
lni-cloud
lni-direction
lni-cloud-check
lni-cloud-sync
lni-cloud-upload
lni-cloudnetwork
lni-cloudy-sun
lni-code
lni-code-alt
lni-dinner
lni-cog
lni-diamond
lni-color-pallet
lni-direction-alt
lni-direction-ltr
lni-comment-reply
lni-construction
lni-construction-hammer
lni-control-panel
lni-credit-cards
lni-crop
lni-cross-circle
lni-crown
lni-css
lni-cup
lni-customer
lni-cut
lni-dashboard
lni-database
lni-delivery
lni-direction-rtl
lni-dashboard