This is the critical part. Many websites offer fake JAR files, adware, or even malicious code disguised as Opera Mini. Below are the most trustworthy sources:
On that page, look for the file named opera-mini-45.0.1.jad (the descriptor) and opera-mini-45.0.1.jar . Both are needed for installation on most phones. opera mini 45 java jar download link
The "Download" button was clicked. The progress bar crawled. This is the critical part