Minor accessibility improvements

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

app/soapbox/components/button.js

@@ -66,7 +66,7 @@ export default class Button extends React.PureComponent {
 
     if (this.props.to) {
       return (
-        <Link to={this.props.to}>
+        <Link to={this.props.to} tabIndex={-1}>
           {btn}
         </Link>
       );

app/soapbox/components/modal_root.js

@@ -1,5 +1,6 @@
 import React from 'react';
 import PropTypes from 'prop-types';
+import 'wicg-inert';
 import { injectIntl, FormattedMessage, defineMessages } from 'react-intl';
 import { connect } from 'react-redux';
 import { openModal } from '../actions/modal';

app/styles/components/account-header.scss

@@ -221,6 +221,7 @@
         }
 
         &:hover,
+        &:focus,
         &.active {
           border-bottom: 2px solid var(--primary-text-color);
         }