CSS: "upload-file" unintentionally becomes displayed when importing Bootstrap icons

I added the external CSS link @import url('https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css') to custom.css to test Bootstrap icons along with Font Awesome icons and Google icons; then <input id="upload-file" type="file" hidden> in .block-editor became visible as text “Choose file” (with a white background) and “No file chosen” (without a background). I hadn’t seen this input element displayed in the default theme or the Dracula theme. Now that it’s displayed, when I click the text, it just disappears by changing .editor-wrapper to .block-content-wrapper. Clicking inside the block to enter the edit mode makes it appear again. When displayed, this <input> has the attribute hidden without a value. According to the inspector, it has also -

input[type=file] {
    display: block;

; clicking the display checkbox off removes/hides “Choose file No file chosen”, as it activates -

[hidden], template {
    display: none;

This unintended display of the text “Choose file No file chosen” occurs only when importing Bootstrap icons, not when importing Google icons or Font Awesome icons. Using Chrome. Is this a bug?