Add stylesheet.

biscuit/apps/chronos/static/css/chronos/timetable.css

+.chronos-lesson {
+    height: 6em;
+}

biscuit/apps/chronos/templates/chronos/tt_week.html

 {# -*- engine:django -*- #}
 {% extends "core/base.html" %}
-{% load bootstrap4 data_helpers i18n %}
+{% load bootstrap4 data_helpers i18n staticfiles %}
+
+{% block bootstrap4_extra_head %}
+ {{ block.super }}
+ <link rel="stylesheet" href="{% static 'css/chronos/timetable.css' %}" />
+{% endblock %}
 
 {% block page_title %}Timetable{% endblock %}