* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
:root {
    font-size: 62.5%;
}

body {
    background-color: #eee;
    color: #345;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    padding: 8px;
}

h1 {
    width: 700px;
    text-align: center;
    margin: 10px auto;
}

.table_hours {
    width: 700px;
    margin: 100px auto;
    font-size: 1.4em;
    border-collapse: collapse;
}

thead th {
    font-weight: bold;
    text-align: left;
}

tbody th {
    font-weight: normal;
    color: #119;
    text-align: left;
}

th, td {
    border-bottom: 1px solid #222;
    padding: 16px 8px;
}

.table_hours tbody tr:last-child th, 
.table_hours tbody tr:last-child td {
    border-bottom: 0;
} 

.table_hours tbody th:hover {
    background-color: lightgreen;
}

.table_hours tbody td {
    background-color: lightgreen;
    border-bottom: 1px solid #eee;
}