Calibre Remaining Pages Helper (Starting with Calibre 4.22 - Select one).

Current of Totals/Current of Section:
<footer style="justify-content: center;font-size:x-small">
<div></div>
<script>document.currentScript.parentNode.querySelector("div").innerHTML =  ""+ _PAGENUM_ +" of " + _TOTAL_PAGES_ + " / " +_TOP_LEVEL_SECTION_PAGENUM_ + " of " + _TOP_LEVEL_SECTION_PAGES_ </script>
</footer>

Current of Totals/Current of Section (With read %):
<footer style="justify-content: center;font-size:x-small">
<div></div>
<script>document.currentScript.parentNode.querySelector("div").innerHTML =  ""+ _PAGENUM_ +" of " + _TOTAL_PAGES_ +" (" + parseInt(_PAGENUM_*100/_TOTAL_PAGES_) + "%) / " +_TOP_LEVEL_SECTION_PAGENUM_ + " of " + _TOP_LEVEL_SECTION_PAGES_ + " ("+ parseInt(_TOP_LEVEL_SECTION_PAGENUM_*100/_TOP_LEVEL_SECTION_PAGES_) +"%)"</script>
</footer>


Remaining of Totals/Remaining of Section:
<footer style="justify-content: center;font-size:x-small">
<div></div>
<script>document.currentScript.parentNode.querySelector("div").innerHTML =  ""+ (_TOTAL_PAGES_ - _PAGENUM_ + 1 ) +" of " + _TOTAL_PAGES_ + " / " +(_TOP_LEVEL_SECTION_PAGES_ - _TOP_LEVEL_SECTION_PAGENUM_ +1 ) + " of " + _TOP_LEVEL_SECTION_PAGES_ </script>
</footer>


Remaining of Totals/Remaining of Section (With % remaining):
<footer style="justify-content: center;font-size:x-small">
<div></div>
<script>document.currentScript.parentNode.querySelector("div").innerHTML =  ""+ (_TOTAL_PAGES_ - _PAGENUM_ + 1 ) +" of " + _TOTAL_PAGES_ + " (" + parseInt((_TOTAL_PAGES_ - _PAGENUM_ + 1 )*100/_TOTAL_PAGES_) + "%) / " +(_TOP_LEVEL_SECTION_PAGES_ - _TOP_LEVEL_SECTION_PAGENUM_ + 1 ) + " of " + _TOP_LEVEL_SECTION_PAGES_ + " (" + parseInt((_TOP_LEVEL_SECTION_PAGES_ - _TOP_LEVEL_SECTION_PAGENUM_ + 1 )*100/_TOP_LEVEL_SECTION_PAGES_) + "%)"</script>
</footer>