Added warning messages when date outside of lecture period

src/components/view/Courses.jsx

@@ -3,6 +3,7 @@ import { format } from 'date-fns'
 import _ from 'lodash'
 import { useEffect, useRef, useState } from 'preact/hooks'
 import { prettyCourseName, WEEK_DAYS } from '../../utils.jsx'
+import { Icon } from '../Icon.jsx'
 
 export const Courses = ({
     source,
@@ -53,7 +54,7 @@ export const Courses = ({
     return (
         <div class="course-view" ref={element}>
             {hideOtherCourses && selection.length === 0 && (
-                <div class="no-courses-warning">
+                <div class="warning">
                     <p>Non hai ancora selezionato nessun corso.</p>
                     <p>
                         Clicca sui corsi nelle altre visuali per selezionarli e