Change icons in web UI (#27385)

Co-authored-by: Renaud Chaput <renchap@gmail.com>

app/javascript/mastodon/components/column_back_button_slim.jsx

@@ -1,5 +1,7 @@
 import { FormattedMessage } from 'react-intl';
 
+import { ReactComponent as ArrowBackIcon } from '@material-symbols/svg-600/outlined/arrow_back.svg';
+
 import { Icon }  from 'mastodon/components/icon';
 
 import ColumnBackButton from './column_back_button';
@@ -10,7 +12,7 @@ export default class ColumnBackButtonSlim extends ColumnBackButton {
     return (
       <div className='column-back-button--slim'>
         <div role='button' tabIndex={0} onClick={this.handleClick} className='column-back-button column-back-button--slim-button'>
-          <Icon id='chevron-left' className='column-back-button__icon' fixedWidth />
+          <Icon id='chevron-left' icon={ArrowBackIcon} className='column-back-button__icon' />
           <FormattedMessage id='column_back_button.label' defaultMessage='Back' />
         </div>
       </div>