[3.1.190618.2-rc1] - HTLC - very hard to change fee asset in mobile version

**Describe the bug**
It's almost impossible to change the fee asset due to the pop-up keyboard (standard and google keyboard).

**To Reproduce**
Steps to reproduce the behavior:
1. Go to [staging.bitshares.org/#/htlc](https://staging.bitshares.org/#/htlc) in mobile browser
2. Click on 'Create HTLC'
3. Try to change fee asset

**Expected behavior**
Easy change of fee asset

**Screenshots**

**Smartphone (please complete the following information):**
- Android 5.1.1 (MIUI Global 7.2) / Android 9
- Standart browser v10.4.5 / Chrome 75
- Swiftkey/Gboard

Open the staging HTLC entry point at staging.bitshares.org/#/htlc in Android browsers and reproduce the issue through Create HTLC, focusing on changing the fee asset while the keyboard is visible. Compare the behavior in the listed standard browser, Chrome, SwiftKey, and Gboard environments; done means the fee asset can be changed easily without the keyboard preventing interaction.

Written by the indexing model from the issue text.