Font size being large when overflow-y is auto or scroll

Dear Sir/Madam,

I am using the Blocs version 3.5.8, I am not sure whether it is the bug from Blocs or the CSS itself. I make two div with overflow-y as hidden and scroll respectively, the font is being large if overflow-y is scroll on Android device only. My Android is Samsung A8+ and running the Android 9

Here is the style of upper DIV
<div id="screen1" style="position: fixed; width: 100vw; height: 49vh; top: 0; left: 0; background-color: black; opacity: 0.9; overflow-y: scroll;" class="pb-5">

Here is the style of lower DIV
<div id="screen2" style="position: fixed; width: 100vw; height: 49vh; bottom: 0; left: 0; background-color: #c0c0c0; opacity: 0.9; overflow-y: hidden;" class="pb-5">

Here is the content same to both DIV

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